C 2018
Notebookcheck

Asus ZenFone 2 Smartphone Review

4 GB of RAM! We all knew it was inevitable, but it's finally here -- the first major consumer smartphone with 4 GB dual-channel DDR3 RAM. Not only that, but it can also be had for just $300. Is this 5.5-inch monster enough to lure users away from popular Chinese brands like the OnePlus One?

Test model provided by GearBest.com. The 4 GB Gray model is currently available for $275 with coupon code ASZ4GB.

Asus hit an early home run in the tablet space with the impressive Transformer and MeMo series that eventually won them contracts to produce the first Nexus tablets for Google. Now the manufacturer is trying everything it can to replicate that success in the crowded smartphone space and things are off to a good start -- the ZenFone series has already won the Red Dot Design Award 2015 for best product design.

The ZenFone 2 begins where the 5-inch ZenFone 5 and 6-inch ZenFone 6 left off by offering a 5.5-inch display with high-end specs that sit comfortably between mainstream and flagship phones. The 1080p display and dual-SIM slots are old hat for an international phone, but the ZenFone 2 throws a curve ball with an Intel Atom CPU and a ridiculous 4 GB RAM for a retail price of $300 to $350. A more down-to-Earth configuration with 2 GB and a 5-inch 720p display is also available in the $200 range. Let's see how the leading confguration holds up against the competition.

Asus Zenfone 2 ZE551ML (Zenfone Series)
Graphics adapter
Memory
4096 MB 
, LPDDR3, Dual-Channel
Display
5.5 inch 16:9, 1920 x 1080 pixel, 10-finger capacitive, IPS, Gorilla Glass 3, glossy: yes
Storage
32 GB eMMC Flash, 32 GB 
, 25 GB free
Connections
1 USB 2.0, Audio Connections: 3.5 mm, Card Reader: MicroSD, Sensors: G-Sensor/E-Compass/Gyroscope/Proximity/Ambient Light Sensor
Networking
802.11 a/b/g/n/ac (a/b/g/n/ac), Bluetooth 4.0, 2G: 850/900/1800/1900, 3G: 850/900/1900/2100, 4G: 2100MHz(1)/1900MHz(2)/1800MHz(3)/1700MHz AWS(4)/850MHz(5)/2600MHz(7)/900MHz(8)/700MHz(17)/800MHz(20)
Size
height x width x depth (in mm): 10.9 x 152.5 x 77.2 ( = 0.43 x 6 x 3.04 in)
Battery
11 Wh Lithium-Polymer, 3000 mAh
Operating System
Android 5.0 Lollipop
Camera
Webcam: Rear: 13 MP, Auto Focus, Front: 5 MP, Fix Focus, Wide View
Additional features
Speakers: Mono, Keyboard: Virtuell, Quick Start guide, Micro-USB charger, Power adapter, Easy Mode, MiniMovie, Asus Help, WebStorage, 12 Months Warranty
Weight
170 g ( = 6 oz / 0.37 pounds), Power Supply: 25 g ( = 0.88 oz / 0.06 pounds)
Price
349 Euro
Note: The manufacturer may use components from different suppliers including display panels, drives or memory sticks with similar specifications.

 

Case

Asus calls the ZenFone 2 "... the best looking smartphone, ever." As subjective as that may be, it's hard to argue against the attractive brushed metallic look of the back cover, especially in those inevitable macro shots of the device. The curved back only accentuates the reflections and shares visual similarities to the costlier LG G3 and HTC One M9. Meanwhile, the front face is the usual Gorilla Glass glossy fare with a 72 percent screen-to-body ratio and more brushed metallic texture work on the bottom for good measure. Users who have had hands-on time with the ZenFone 5 or ZenFone 6 will know exactly what to expect here as the overall design philosophy and appearance remain largely unchanged. The notable exception is the Volume rocker, which is now on the back of the device a la the LG G2 and G3.

Unfortunately, "metallic look" in this case is just a fancy way of saying "plastic" or "polycarbonate". When removed, the back cover bends and twists as easily as any other plastic cover and is not a true aluminum alloy as are the covers on the HTC One M8 and M9. Edges and corners feel soft and will ding more easily than alloyed smartphones. With that said, the ZenFone 2 is still rigid with no creaking or visible depressions and only minimal twisting overall. As is a common feature with removable back covers, multiple colors are available for added customization.

Its arched back gives the ZenFone 2 a maximum thickness of almost 11 mm (or 3.9 mm around the thin edges), which is thicker than all other 5.5-inch smartphones in our comparison graphic below. Weight is luckily in line with what we expect from a device this size at about 170 g compared to the iPhone 6 Plus (172 g), OnePlus One (164 g), and LG G Flex 2 (152 g).

Connectivity

Physical connectivity ports include the usual USB 2.0 on bottom and 3.5 mm audio on top. As with most Android devices since Honeycomb, USB OTG is supported and we were able to connect generic mice and and keyboards without issues. We also tried a MHL USB-HDMI adapter on the off-chance that it may work, but to no success.

Bottom: Micro-USB 2.0 port, Microphone
Bottom: Micro-USB 2.0 port, Microphone
Right: No connectivity
Right: No connectivity
Top: 3.5 mm audio, Power button
Top: 3.5 mm audio, Power button
Left: No connectivity
Left: No connectivity

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Software

ZenUI is the exclusive front-end interface for most smartphones and tablets from Asus. It's not as far-reaching as the recent Sense makeover from HTC and is actually quite light in terms of custom settings and animations, but it does add a couple of useful features. In particular, ZenMotion makes it quick to open any preset application without needing to wake the display by drawing a letter or command on the blank screen, while Easy Mode is perfect for entry-level users who have no need for extra features and prefer fewer and larger icons. Finally, ZenLink encompasses both remote PC and local connections through WiFi or Bluetooth.

The overall feel is otherwise Android 5.0 at its core with minimal fluff. There is of course the wave of pre-loaded apps as expected from any Android software suite.

Standard phone number pad
Standard phone number pad
Dropdown menu and features
Dropdown menu and features
Multiple display color modes and customization
Multiple display color modes and customization
Handy ZenMotion launches apps by "drawing" letters onscreen
Handy ZenMotion launches apps by "drawing" letters onscreen
Default Android 5.0 homescreen
Default Android 5.0 homescreen
"Easy Mode" feature reduces icons to the bare basics
"Easy Mode" feature reduces icons to the bare basics
Asus Lock screen with notifications and shortcuts
Asus Lock screen with notifications and shortcuts
DU app is just one of many pre-installed adware from GearBest
DU app is just one of many pre-installed adware from GearBest

Communication & GPS

Wireless connections include 802.11ac with Bluetooth 4.0, NFC, and Miracast (via the PlayTo function). We experienced no dropout or limited range issues when connected to a standard WLAN network. Compared to a LG G2, the Asus shows slightly better signal strength and consistent connection under the same network and conditions.

The built-in GPS works as expected with a faster TTFF compared to the LG G2. It is also able to take advantage of more satellites in view, which should lower the chances of signal loss during use.

LG G2 GPS Test
LG G2 GPS Test
Asus ZenFone 2 GPS Test
Asus ZenFone 2 GPS Test
LG G2 WiFi Signal ~10 m from source
LG G2 WiFi Signal ~10 m from source
Asus ZenFone 2 WiFi Signal ~10 m from source
Asus ZenFone 2 WiFi Signal ~10 m from source

Telephone & Speech Quality

Compatible bands are wide and varied and too great to list here -- we refer to the official Asus specifications for the full list of 2G, 3G, and 4G bands. The bottom line for U.S. users is that the ZenFone 2 will work with the two biggest GSM carriers: AT&T and T-Mobile. Verizon, Sprint, and other CDMA carriers are not officially supported. We were able to use both 3G and 4G with our own AT&T and T-Mobile SIM cards.

Since the battery is non-removable, both Micro SIM slots are accessible without needing to power down the device. However, Asus makes it very clear that only one slot supports 2G, 3G, and 4G bands, while the second slot supports up to 2G.

Call quality with full bars sounds good from both ends. Our LG G2 receiver on the other end is able to hear very clearly with no breaks, though voices carry more static to the listener on the ZenFone 2. Fortunately, it's not enough to significantly impact user experience. Reception is largely not an issue, at least with AT&T in San Francisco.

Similar setup as the older ZenFone 5 and ZenFone 6 with an added MicroSD slot
Similar setup as the older ZenFone 5 and ZenFone 6 with an added MicroSD slot

Cameras

The rear 13 MP (4096 x 3072) camera uses the standard f/2.0 aperture that most other smartphones have with the usual ISO (50 to 800), auto-focus, HDR, and face detection features. There is also a full Manual mode to mimic DSLR features, though this setup offers little more than the default camera mode. Certain 2 GB ZenFone 2 models will only have 2 MP and 8 MP front- and rear-facing cameras, respectively, compared to 5 MP and 13 MP Toshiba sensors on our higher-end configuration.

Camera quality is good in terms of colors with no hints of purple fringing when used outdoors. Instead, sharpness is the issue as the ZenFone is unable to accurately capture hard corners and edges of objects as well as competing cameraphones. Smaller details and textures of surfaces will be comparatively more blurred.

Low Light Mode reduces captured images to 3 MP and increases shutter time. Flash is disabled in this mode and while this does significantly improve natural lighting for a picture, overall quality becomes much more washed out as opposed to just using the standard Flash. In fact, the built-in Flash is powerful enough for low-distance shooting and is the preferable option.

Video recording supports up to 1080p30 and files are saved as MP4 with a content bit rate of about 15000 kb/s. Similar to snapshots taken with the ZenFone 2, video quality could be more crisp with less blurring when panning. In other words, the Asus brings nothing special here.

Accessories & Warranty

The box includes the standard Quick Start guide, Micro-USB charger, and power adapter. Users aren't treated to any neat extras like screen protectors, earphones, or additional back covers. Instead, Asus offers these as optional accessories including Flash and selfie add-ons designed specifically for the ZenFone.

Asus warranty is the standard 12-month period from date of purchase. The manufacturer does not cover dead pixels and does not offer extended warranty options by registering the device.

Input Devices & Interface

It's unfortuante how so many inexpensive smartphones can implement touchscreen responsiveness and latency so poorly. Inaccurate inputs, lag for fast typists, and missed keys are enough to ruin even the best-looking devices. This is fortunately not the case for the ZenFone 2 as inputs are registered just as fast as we can humanly type on the included virtual keyboard. The touchscreen is as responsive and precise around the edges and corners as it is on the center, which is not something we can say for all phones.

As for the onscreen keyboard, it is the same one included with the ZenFone 5 and ZenFone 6. Users have all the standard options such as word prediction, Swype-like functionality, and keyboard height adjustments. Users may want to tone down the latter as the default keyboard height is a bit too high to comfortably read SMS texts.

Also of note are the dedicated Back, Home, and Tabs buttons common amongst Android devices. This frees up valuable onscreen real-estate at the cost of a larger bezel. This is perhaps best exemplified by the noticeable discrepancy in length between the 5.5-inch LG G3 and ZenFone 2 (74.6 mm vs. 77.2 mm).

Essentially the same keyboard skin and interface of the larger ZenFones
Essentially the same keyboard skin and interface of the larger ZenFones
Swype not enabled by default
Swype not enabled by default

Display

Needless to say, the 5.5-inch 1080p display is spectacular and easier on the eyes compared to smaller 5-inch 1080p models. Images and texts are crisp on their own right, but certainly not as sharp as the increasingly common 1440p displays on flagship phones like the G3 or Galaxy S6. The screen itself is also under a seemingly thicker layer of glass, so colors do not pop as much as they would on an iPhone 6 Plus.

Measured black levels are low for a very good contrast of about 1000:1, which is comparable to competing models. Screen brightness is the low point of the device at an average of just over 300 nits compared to over 400 nits on other major 5.5-inch models. While not bad and certainly sufficient for indoor use, this makes the ZenFone a poorer choice for outdoor use.

306.4
cd/m²
325
cd/m²
312.3
cd/m²
298.4
cd/m²
329.4
cd/m²
315
cd/m²
295.8
cd/m²
333.5
cd/m²
317
cd/m²
Distribution of brightness
X-Rite i1Basic Pro 2
Maximum: 333.5 cd/m² Average: 314.8 cd/m²
Brightness Distribution: 89 %
Center on Battery: 329.4 cd/m²
Contrast: 1105:1 (Black: 0.298 cd/m²)
ΔE Color 5.24 | 0.4-29.43 Ø6.3
ΔE Greyscale 4.8 | 0.64-98 Ø6.5
Gamma: 2.43
Asus Zenfone 2 ZE551MLApple iPhone 6 PlusOnePlus OneLG G Flex 2Xiaomi Redmi Note 4GLG G3
Screen
5%
-17%
-23%
-4%
-37%
Brightness middle
329.4
519
58%
423
28%
278
-16%
446
35%
417
27%
Brightness
315
496
57%
408
30%
274
-13%
418
33%
395
25%
Brightness Distribution
89
90
1%
83
-7%
97
9%
87
-2%
89
0%
Black Level *
0.298
0.62
-108%
0.54
-81%
0.47
-58%
0.96
-222%
Contrast
1105
837
-24%
783
-29%
949
-14%
434
-61%
Colorchecker DeltaE2000 *
5.24
3.67
30%
5.56
-6%
8.03
-53%
5.1
3%
5.67
-8%
Greyscale DeltaE2000 *
4.8
3.78
21%
7.55
-57%
6.71
-40%
5.93
-24%
5.66
-18%
Gamma
2.43 91%
2.42 91%
2.33 94%
1.89 116%
3.46 64%
2.53 87%
CCT
7419 88%
7327 89%
7624 85%
7750 84%
7350 88%
7741 84%
Color Space (Percent of AdobeRGB 1998)
59

* ... smaller is better

Color analyses with a spectrophotometer reveal generally accurate colors across all tested saturation levels. Colors do not become increasingly less accurate with increasing or decreasing saturation. The screen also avoids an overly blue temperature that commonly plagues cheaper phones.

Of particular note is that the ZenFone 2 offers four different color modes: Balance, Reading, Vivid, and Customized. As shown in our measurements below, Balance offers the most accurate colors against the sRGB standard. Reading mode will drop correlated color temperature from around 7K to 6K for a warmer picture, while Vivid mode brightens colors at the cost of accuracy. Lastly, the Customized mode allows users to manually change the Hue and Saturation at will.

Grayscale - Balanced Profile
Grayscale - Balanced Profile
Saturation Sweeps - Balanced Profile
Saturation Sweeps - Balanced Profile
ColorChecker - Balanced Profile
ColorChecker - Balanced Profile
Grayscale - Reading Profile
Grayscale - Reading Profile
Saturation Sweeps - Reading Profile
Saturation Sweeps - Reading Profile
ColorChecker - Reading Profile
ColorChecker - Reading Profile
Grayscale - Vivid Profile
Grayscale - Vivid Profile
Saturation Sweeps - Vivid Profile
Saturation Sweeps - Vivid Profile
ColorChecker - Vivid Profile
ColorChecker - Vivid Profile

Outdoor usability is acceptable, but the maximum brightness setting is essentially required as the backlight is weaker than on competing models. Shade or overcast days are best as using the ZenFone 2 under direct sunlight for extended periods will become uncomfortable.

It is also recommended to disable the Asus Smart Battery feature when outdoors. Otherwise, maximum display brightness will be limited to just 160 nits.

Great visibility under shade, but merely average on overcast days
Great visibility under shade, but merely average on overcast days
Wide viewing angles from IPS panel
Wide viewing angles from IPS panel

Performance

Asus equips the ZenFone 2 with not one, or two, but three different Intel Atom processors to choose from. The lowest configuration uses the dual-core 1.6 GHz Atom Z2560 with weaker PowerVR SGX544MP2 graphics, while the middle and high-end configurations are equipped with a quad-core 1.8 GHz Atom Z3560 and 2.3 GHz Atom Z3580, respectively. Our in-house model uses the more mainstream Atom Z3560, which is the same processor as found on the FonePad 7 and a number of MeMo tablets from Asus.

General system performance is very fast with little lag time when multi-tasking between applications. Raw CPU performance is just a step below the high-end Snapdragon 800 series found on flagship smartphones. According to CPU-Z, the Z3560 in our ZenFone 2 can operate up to its rated 1.83 GHz for all cores simultaneously, though this is rare as all cores will normally operate in the 500 to 1333 MHz range for most tasks. No cores here are ever disabled when the display is on and active.

The 4 GB RAM allows for an insane number of simultaneous applications. CPU-Z records about 2.4 GB of free RAM when no other applications are running, and this is including all the default adware and background applications that may be active. Asus claims about 1.5x faster multi-tasking performance compared to 2 GB smartphones when at least 26 applications are running. Most users may never feel a difference, but users who don't periodically manage the inevitable buildup of junk applications may benefit from the additional headroom.

PCMark for Android - Work performance score (sort by value)
Asus Zenfone 2 ZE551ML
5083 Points ∼38%
Asus Fonepad Note FHD 6 ME560CG (K00G)
3678 (min: 3520, max: 3977) Points ∼28% -28%
OnePlus One
3571 Points ∼27% -30%
HTC One M9
4193 Points ∼32% -18%
Google Nexus 9
5841 Points ∼44% +15%
Sunspider
1.0 Total Score (sort by value)
Asus Zenfone 2 ZE551ML
817.7 ms * ∼20%
Asus Fonepad Note FHD 6 ME560CG (K00G)
857.1 ms * ∼21% -5%
OnePlus One
2180.1 ms * ∼54% -167%
HTC One M9
839.7 ms * ∼21% -3%
Apple iPhone 6 Plus
347.4 ms * ∼9% +58%
Google Nexus 9
919.3 ms * ∼23% -12%
0.9.1 Total Score (sort by value)
Asus Zenfone 2 ZE551ML
839.5 ms * ∼8%
Asus Fonepad Note FHD 6 ME560CG (K00G)
921.5 ms * ∼9% -10%
HTC One M9
778.2 ms * ∼7% +7%
Apple iPhone 6 Plus
361.8 ms * ∼3% +57%
Google Nexus 9
924.7 ms * ∼9% -10%
Google V8 Ver. 7 - Google V8 Ver. 7 Score (sort by value)
Asus Zenfone 2 ZE551ML
6198 Points ∼32%
Asus Fonepad Note FHD 6 ME560CG (K00G)
3857 Points ∼20% -38%
OnePlus One
4681 Points ∼24% -24%
HTC One M9
6440 Points ∼33% +4%
Apple iPhone 6 Plus
8604 Points ∼44% +39%
Google Nexus 9
10142 Points ∼52% +64%
Octane V2 - Total Score (sort by value)
Asus Zenfone 2 ZE551ML
6507 Points ∼13%
HTC One M9
6493 Points ∼13% 0%
Apple iPhone 6 Plus
7276 Points ∼15% +12%
Google Nexus 9
8210 Points ∼17% +26%
Mozilla Kraken 1.1 - Total Score (sort by value)
Asus Zenfone 2 ZE551ML
5845.9 ms * ∼10%
Asus Fonepad Note FHD 6 ME560CG (K00G)
10624.5 ms * ∼18% -82%
OnePlus One
7883 ms * ∼13% -35%
HTC One M9
6508.2 ms * ∼11% -11%
Apple iPhone 6 Plus
4469.8 ms * ∼8% +24%
Google Nexus 9
4030.5 ms * ∼7% +31%
WebXPRT 2013
Offline Notes (sort by value)
Asus Zenfone 2 ZE551ML
927 ms * ∼19%
Asus Fonepad Note FHD 6 ME560CG (K00G)
1029.2 ms * ∼21% -11%
OnePlus One
1799 ms * ∼38% -94%
HTC One M9
1132.1 ms * ∼24% -22%
Apple iPhone 6 Plus
499 ms * ∼10% +46%
Google Nexus 9
900 ms * ∼19% +3%
Stocks Dashboard (sort by value)
Asus Zenfone 2 ZE551ML
721.7 ms * ∼19%
Asus Fonepad Note FHD 6 ME560CG (K00G)
942.9 ms * ∼25% -31%
OnePlus One
1488.1 ms * ∼40% -106%
HTC One M9
1087.6 ms * ∼29% -51%
Apple iPhone 6 Plus
338 ms * ∼9% +53%
Google Nexus 9
765.7 ms * ∼20% -6%
Face Detection (sort by value)
Asus Zenfone 2 ZE551ML
1227.2 ms * ∼10%
Asus Fonepad Note FHD 6 ME560CG (K00G)
5243 ms * ∼43% -327%
OnePlus One
2123.9 ms * ∼18% -73%
HTC One M9
2237.3 ms * ∼18% -82%
Apple iPhone 6 Plus
1463.2 ms * ∼12% -19%
Google Nexus 9
810.4 ms * ∼7% +34%
Photo Effects (sort by value)
Asus Zenfone 2 ZE551ML
681.5 ms * ∼8%
Asus Fonepad Note FHD 6 ME560CG (K00G)
1912.7 ms * ∼21% -181%
OnePlus One
945.7 ms * ∼11% -39%
HTC One M9
1585.1 ms * ∼18% -133%
Apple iPhone 6 Plus
904.7 ms * ∼10% -33%
Google Nexus 9
576.2 ms * ∼6% +15%
Overall Score (sort by value)
Asus Zenfone 2 ZE551ML
480 Points ∼21%
Asus Fonepad Note FHD 6 ME560CG (K00G)
236 Points ∼10% -51%
OnePlus One
273 Points ∼12% -43%
HTC One M9
287 Points ∼13% -40%
Apple iPhone 6 Plus
604 Points ∼27% +26%
Google Nexus 9
552 Points ∼24% +15%
WebXPRT 2015 - Overall Score (sort by value)
Asus Zenfone 2 ZE551ML
109 Points ∼14%
HTC One M9
72 Points ∼9% -34%
Peacekeeper - --- (sort by value)
Asus Zenfone 2 ZE551ML
837 Points ∼14%
Asus Fonepad Note FHD 6 ME560CG (K00G)
734 Points ∼12% -12%
OnePlus One
760 Points ∼12% -9%
HTC One M9
1043 Points ∼17% +25%
Apple iPhone 6 Plus
2613 Points ∼42% +212%
Google Nexus 9
2387 Points ∼39% +185%
BaseMark OS II
Web (sort by value)
Asus Zenfone 2 ZE551ML
688 Points ∼40%
Asus Fonepad Note FHD 6 ME560CG (K00G)
366 Points ∼21% -47%
OnePlus One
661 Points ∼38% -4%
HTC One M9
789 Points ∼46% +15%
Apple iPhone 6 Plus
1092 Points ∼63% +59%
Google Nexus 9
516 Points ∼30% -25%
Graphics (sort by value)
Asus Zenfone 2 ZE551ML
1432 Points ∼9%
Asus Fonepad Note FHD 6 ME560CG (K00G)
360 Points ∼2% -75%
OnePlus One
2382 Points ∼15% +66%
HTC One M9
3210 Points ∼20% +124%
Apple iPhone 6 Plus
2389 Points ∼15% +67%
Google Nexus 9
8602 Points ∼54% +501%
Memory (sort by value)
Asus Zenfone 2 ZE551ML
954 Points ∼20%
Asus Fonepad Note FHD 6 ME560CG (K00G)
354 Points ∼7% -63%
OnePlus One
587 Points ∼12% -38%
HTC One M9
933 Points ∼19% -2%
Apple iPhone 6 Plus
536 Points ∼11% -44%
Google Nexus 9
1509 Points ∼31% +58%
System (sort by value)
Asus Zenfone 2 ZE551ML
1622 Points ∼13%
Asus Fonepad Note FHD 6 ME560CG (K00G)
741 Points ∼6% -54%
OnePlus One
1768 Points ∼14% +9%
HTC One M9
1672 Points ∼14% +3%
Apple iPhone 6 Plus
2038 Points ∼17% +26%
Google Nexus 9
1729 Points ∼14% +7%
Overall (sort by value)
Asus Zenfone 2 ZE551ML
1111 Points ∼18%
Asus Fonepad Note FHD 6 ME560CG (K00G)
431 Points ∼7% -61%
OnePlus One
1131 Points ∼19% +2%
HTC One M9
1410 Points ∼23% +27%
Apple iPhone 6 Plus
1299 Points ∼21% +17%
Google Nexus 9
1845 Points ∼30% +66%
AndEBench
Java (sort by value)
Asus Zenfone 2 ZE551ML
1096 Iter./s ∼34%
Asus Fonepad Note FHD 6 ME560CG (K00G)
265 Iter./s ∼8% -76%
HTC One M9
1400 Iter./s ∼43% +28%
Google Nexus 9
1420 Iter./s ∼44% +30%
Native (sort by value)
Asus Zenfone 2 ZE551ML
16601 Iter./s ∼54%
Asus Fonepad Note FHD 6 ME560CG (K00G)
11714 Iter./s ∼38% -29%
HTC One M9
15384 Iter./s ∼50% -7%
Google Nexus 9
10094 Iter./s ∼33% -39%
ANDEBench PRO
3D (sort by value)
Asus Zenfone 2 ZE551ML
18.22 fps ∼14%
OnePlus One
24.6 fps ∼19% +35%
HTC One M9
32.88 fps ∼25% +80%
Platform (sort by value)
Asus Zenfone 2 ZE551ML
185.5 Points ∼3%
OnePlus One
140.6 Points ∼2% -24%
HTC One M9
154.1 Points ∼2% -17%
Storage (sort by value)
Asus Zenfone 2 ZE551ML
5939 KB/s ∼6%
OnePlus One
7193 KB/s ∼7% +21%
HTC One M9
5862 KB/s ∼6% -1%
Memory Latency (sort by value)
Asus Zenfone 2 ZE551ML
5649 KOps/s ∼70%
OnePlus One
6738 KOps/s ∼83% +19%
HTC One M9
2302 KOps/s ∼29% -59%
Memory Bandwidth (sort by value)
Asus Zenfone 2 ZE551ML
4074 MB/s ∼19%
OnePlus One
5485 MB/s ∼26% +35%
HTC One M9
7609 MB/s ∼36% +87%
CoreMark-PRO/HPC (Base) (sort by value)
Asus Zenfone 2 ZE551ML
2718 Points ∼42%
OnePlus One
2464 Points ∼38% -9%
HTC One M9
2296 Points ∼36% -16%
Device Score (sort by value)
Asus Zenfone 2 ZE551ML
6911 Points ∼27%
OnePlus One
7169 Points ∼27% +4%
HTC One M9
7158 Points ∼27% +4%
Vellamo 3.x
Metal (sort by value)
Asus Zenfone 2 ZE551ML
1200 Points ∼32%
Asus Fonepad Note FHD 6 ME560CG (K00G)
900 Points ∼24% -25%
OnePlus One
1622 Points ∼43% +35%
HTC One M9
2280 Points ∼61% +90%
Google Nexus 9
2754 Points ∼74% +130%
Multicore Beta (sort by value)
Asus Zenfone 2 ZE551ML
1251 Points ∼28%
Asus Fonepad Note FHD 6 ME560CG (K00G)
1230 Points ∼27% -2%
OnePlus One
1771 Points ∼39% +42%
HTC One M9
2298 Points ∼51% +84%
Google Nexus 9
2642 Points ∼59% +111%
Browser (sort by value)
Asus Zenfone 2 ZE551ML
3005 Points ∼40%
Asus Fonepad Note FHD 6 ME560CG (K00G)
1834 Points ∼24% -39%
OnePlus One
2683 Points ∼35% -11%
HTC One M9
3174 Points ∼42% +6%
Google Nexus 9
6263 Points ∼83% +108%
Epic Citadel
Ultra High Quality (sort by value)
Asus Zenfone 2 ZE551ML
44.4 fps ∼72%
Asus Fonepad Note FHD 6 ME560CG (K00G)
34.8 fps ∼56% -22%
OnePlus One
50.1 fps ∼81% +13%
HTC One M9
58.2 fps ∼94% +31%
Google Nexus 9
58.5 fps ∼95% +32%
High Quality (sort by value)
Asus Zenfone 2 ZE551ML
58.3 fps ∼96%
Asus Fonepad Note FHD 6 ME560CG (K00G)
57.7 fps ∼95% -1%
OnePlus One
56 fps ∼92% -4%
Google Nexus 9
52.1 fps ∼86% -11%
High Performance (sort by value)
Asus Zenfone 2 ZE551ML
58.4 fps ∼96%
Asus Fonepad Note FHD 6 ME560CG (K00G)
59.1 fps ∼97% +1%
OnePlus One
57.1 fps ∼94% -2%
Google Nexus 9
52 fps ∼86% -11%
AndroBench 3-5
Random Write 4KB (sort by value)
Asus Zenfone 2 ZE551ML
5.91 MB/s ∼4%
Asus Fonepad Note FHD 6 ME560CG (K00G)
0.98 MB/s ∼1% -83%
OnePlus One
10.42 MB/s ∼6% +76%
HTC One M9
13.91 MB/s ∼8% +135%
Google Nexus 9
14.49 MB/s ∼9% +145%
Random Read 4KB (sort by value)
Asus Zenfone 2 ZE551ML
22.69 MB/s ∼13%
Asus Fonepad Note FHD 6 ME560CG (K00G)
10.31 MB/s ∼6% -55%
OnePlus One
18.27 MB/s ∼11% -19%
HTC One M9
20.66 MB/s ∼12% -9%
Google Nexus 9
36.22 MB/s ∼21% +60%
Sequential Write 256KB (sort by value)
Asus Zenfone 2 ZE551ML
54.6 MB/s ∼23%
Asus Fonepad Note FHD 6 ME560CG (K00G)
13.74 MB/s ∼6% -75%
OnePlus One
159.72 MB/s ∼66% +193%
HTC One M9
123.81 MB/s ∼51% +127%
Google Nexus 9
75.49 MB/s ∼31% +38%
Sequential Read 256KB (sort by value)
Asus Zenfone 2 ZE551ML
147.56 MB/s ∼16%
Asus Fonepad Note FHD 6 ME560CG (K00G)
69.6 MB/s ∼8% -53%
OnePlus One
223.64 MB/s ∼25% +52%
HTC One M9
235.14 MB/s ∼26% +59%
Google Nexus 9
279.16 MB/s ∼31% +89%
3DMark
2560x1440 Sling Shot Extreme (ES 3.1) Physics (sort by value)
HTC One M9
1132 Points ∼27%
2560x1440 Sling Shot Extreme (ES 3.1) Graphics (sort by value)
HTC One M9
1084 Points ∼20%
2560x1440 Sling Shot Extreme (ES 3.1) (sort by value)
HTC One M9
1094 Points ∼23%
2560x1440 Sling Shot OpenGL ES 3.0 Physics (sort by value)
HTC One M9
845 Points ∼20%
2560x1440 Sling Shot OpenGL ES 3.0 Graphics (sort by value)
HTC One M9
1892 Points ∼23%
2560x1440 Sling Shot OpenGL ES 3.0 (sort by value)
HTC One M9
1484 Points ∼23%
1280x720 offscreen Ice Storm Unlimited Physics (sort by value)
Asus Zenfone 2 ZE551ML
16550 Points ∼21%
Asus Fonepad Note FHD 6 ME560CG (K00G)
10809 Points ∼14% -35%
OnePlus One
13167 Points ∼17% -20%
HTC One M9
10432 (min: 10432, max: 10786) Points ∼13% -37%
Apple iPhone 6 Plus
9473 Points ∼12% -43%
Google Nexus 9
12420 Points ∼16% -25%
1280x720 offscreen Ice Storm Unlimited Graphics Score (sort by value)
Asus Zenfone 2 ZE551ML
14270 Points ∼3%
Asus Fonepad Note FHD 6 ME560CG (K00G)
6595 Points ∼1% -54%
OnePlus One
18074 Points ∼4% +27%
HTC One M9
34429 (min: 34429, max: 34485) Points ∼7% +141%
Apple iPhone 6 Plus
23937 Points ∼5% +68%
Google Nexus 9
39070 Points ∼8% +174%
1280x720 offscreen Ice Storm Unlimited Score (sort by value)
Asus Zenfone 2 ZE551ML
14721 Points ∼7%
Asus Fonepad Note FHD 6 ME560CG (K00G)
7221 Points ∼3% -51%
OnePlus One
16692 Points ∼8% +13%
HTC One M9
22783 (min: 22783, max: 23171) Points ∼11% +55%
Apple iPhone 6 Plus
17873 Points ∼9% +21%
Google Nexus 9
26455 Points ∼13% +80%
1920x1080 Ice Storm Extreme Physics (sort by value)
Asus Zenfone 2 ZE551ML
7530 Points ∼10%
Asus Fonepad Note FHD 6 ME560CG (K00G)
9915 Points ∼13% +32%
1920x1080 Ice Storm Extreme Graphics (sort by value)
Asus Zenfone 2 ZE551ML
7875 Points ∼1%
Asus Fonepad Note FHD 6 ME560CG (K00G)
3754 Points ∼1% -52%
1920x1080 Ice Storm Extreme Score (sort by value)
Asus Zenfone 2 ZE551ML
7796 Points ∼4%
Asus Fonepad Note FHD 6 ME560CG (K00G)
4355 Points ∼2% -44%
1280x720 Ice Storm Standard Physics (sort by value)
Asus Fonepad Note FHD 6 ME560CG (K00G)
9672 Points ∼6%
1280x720 Ice Storm Standard Graphics (sort by value)
Asus Fonepad Note FHD 6 ME560CG (K00G)
6843 Points ∼1%
1280x720 Ice Storm Standard Score (sort by value)
Asus Fonepad Note FHD 6 ME560CG (K00G)
7319 Points ∼1%
Lightmark - 1920x1080 1080p (sort by value)
Asus Zenfone 2 ZE551ML
7.61 fps ∼20%
OnePlus One
5.33 fps ∼14% -30%
HTC One M9
11.56 fps ∼30% +52%

Legend

 
Asus Zenfone 2 ZE551ML Intel Atom Z3560, PowerVR G6430, 32 GB eMMC Flash
 
Asus Fonepad Note FHD 6 ME560CG (K00G) Intel Atom Z2580, PowerVR SGX544MP2, 16 GB iNAND Flash
 
OnePlus One Qualcomm Snapdragon 801 MSM8974AC, Qualcomm Adreno 330, 64 GB eMMC Flash
 
HTC One M9 Qualcomm Snapdragon 810 MSM8994, Qualcomm Adreno 430, 32 GB eMMC Flash
 
Apple iPhone 6 Plus Apple A8, PowerVR GX6450, 64 GB eMMC Flash
 
Google Nexus 9 Nvidia Tegra K1 (Denver), NVIDIA Tegra K1 Kepler GPU, 32 GB eMMC Flash

* ... smaller is better

Games

The integrated PowerVR G6430 GPU should be similar to the Adreno 320 and Adreno 330 in terms of graphics horsepower. 3DMark Ice Storm and Lightmark benchmarks put our ZenFone 2 clearly ahead of the PowerVR SGX544MP2 in the ZenFone 6 and slightly above the Adreno 330 in the OnePlus One. Nonetheless, it falls short of the current high-end Adreno 430 and Tegra K1 in most graphics benchmarks including Epic Citadel by a wide margin (~45 FPS vs. ~58 FPS).

The high-end Qualcomm and Nvidia GPUs may be overkill for a native 1080p display, so the PowerVR G6430 feels like a more balanced pairing for the ZenFone 2 and is relatively powerful for the price. After all, the Apple iPad Mini 3 utilizes a very similar PowerVR graphics processor. Ice Storm Extreme and 3D titles from the Android Market play very smoothly with no unexpected hiccups or frame skips.

A steady 50 to 60 FPS on Ice Storm Extreme
A steady 50 to 60 FPS on Ice Storm Extreme
3D Android titles play very smoothly
3D Android titles play very smoothly
Intensive Lightmark benchmark at single-digit FPS
Intensive Lightmark benchmark at single-digit FPS

Emissions

Temperature

When idling or under heavy system stress, surface temperatures are not unlike those of the LG Flex 2 or HTC One M9 under similar conditions. Our ZenFone 2 sits in the 22 to 25 C range when idling and can be as warm as 35 C when gaming or running intensive applications for extended periods. Considering our cool room temperature of 18 C during measurements, the temperature delta is more or less similar to Snapdragon 800-powered smartphones of similar size. The exception is the OnePlus One, which can reach surface temperatures as high as 45 C due to its high and very stable GPU performance.

The integrated battery itself is in the low 30s when browsing and will only be as high as 34 to 36 C on higher processing loads.

Max. Load
 34.8 °C
95 F
33.2 °C
92 F
31 °C
88 F
 
 34.2 °C
94 F
32.3 °C
90 F
31.2 °C
88 F
 
 33.8 °C
93 F
32.2 °C
90 F
31.2 °C
88 F
 
Maximum: 34.8 °C = 95 F
Average: 32.7 °C = 91 F
28 °C
82 F
30.6 °C
87 F
35.4 °C
96 F
27.6 °C
82 F
29.6 °C
85 F
33.6 °C
92 F
29.6 °C
85 F
30.8 °C
87 F
33.4 °C
92 F
Maximum: 35.4 °C = 96 F
Average: 31 °C = 88 F
Power Supply (max.)  28.2 °C = 83 F | Room Temperature 18 °C = 64 F | Fluke 62 Mini IR Thermometer

Speakers

Sound quality is essentially unchanged from the ZenFone 5. Bass is adequate for a smartphone with the "tin can" quality still present. Nonetheless, maximum volume is loud and does not add significant static or imbalances. Audio from dedicated earphones will always be the better solution in this case.

Speakerphone on bottom rear of smartphone
Speakerphone on bottom rear of smartphone

Battery Life

The 11.4 Wh battery (3000 mAh) is essentially the same capacity as other 5.5-inch devices including the iPhone 6 Plus (11.1 Wh), LG Flex 2 (11.8 Wh), OnePlus One (11.8 Wh), and the Redmi Note 4G (11.8 Wh). Like the larger ZenFone 6 and smaller ZenFone 5, the battery here is non-removable.

Integrated batteries aren't a huge issue as long as there are long runtimes to make up for it. With the ZenFone 2, users can expect a bit over 6 hours of constant WLAN use on a brightness of 150 nits (~70 percent setting) according to our looping browser script. This is below average compared to the 900+ and 600+ minutes of the OnePlus One and G Flex 2, respectively, when under the same conditions. The ZenFone still dies out more quickly than competing models when sitting idle on the lowest display brightness and with Smart Saving battery mode engaged.

At worst, users can expect about 4 hours of heavy use on maximum brightness. This is notably longer than the the closest competitors, but it's also worth keeping in mind that the display of the ZenFone 2 is not the brightest of the bunch.

Charging time from near depletion to 100 percent will still take a little over 2.5 hours with the included 5.2 V AC adapter. The high-capacity 18 W BoostMaster charger is only included with the 2.3 GHz Atom Z3580 ZenFone 2 model.

Battery Runtime
Idle (without WLAN, min brightness)
16h 59min
NBC WiFi Websurfing Battery Test 1.3
6h 15min
Load (maximum brightness)
4h 15min
Asus Zenfone 2 ZE551MLApple iPhone 6 PlusOnePlus OneLG G Flex 2Xiaomi Redmi Note 4G
Battery Runtime
10%
58%
17%
-22%
Reader / Idle
1019
1436
41%
1568
54%
1274
25%
985
-3%
WiFi v1.3
375
963
157%
641
71%
Load
255
199
-22%
160
-37%
143
-44%
152
-40%
WiFi
777
1126
662

Pros

+ Attractive design
+ Massive 4 GB of RAM
+ Fast system performance
+ 1080p IPS display with high contrast
+ Dual-SIM support
+ Rigid chassis
+ Clear speaker and reception

Cons

- Faux brushed metal; Plastic and polycarbonate materials
- Thicker than competing 5.5-inch models
- Below average battery life
- Average display brightness
- No CDMA version
- Soft pictures from camera
- No USB 3.0 or MHL
- Non-removable battery

Verdict

Asus ZenFone 2. Test model provided by GearBest.com. The 4 GB Gray model is available for $275 with coupon code ASZ4GB
Asus ZenFone 2. Test model provided by GearBest.com. The 4 GB Gray model is available for $275 with coupon code ASZ4GB

For a $200 to $300 smartphone, the ZenFone 2 makes a strong case against more expensive 5.5-inch devices, especially from a design and performance standpoint. The device itself is physically quite large, though no less difficult to grip and use.  It's tough not to like the arched metallic back and the 4 GB RAM should appease users who are hooked on frequently installing applications just to try them while improving device longevity. The 4G and dual-SIM support will also appeal to international users who prefer a more established brand like Asus instead of rising Chinese brands like Xiaomi or Huawei.

Caveats include a backlight that is notably weaker than on competing models and the below average battery life. Granted, 6 hours of constant WiFi use is probably sufficient for most users, but the lack of a removable battery doesn't help it, either. These few major downsides make the similarly-priced OnePlus One an easier recommendation for those who don't see any short-term or long-term benefits of 4 GB RAM.

Asus Zenfone 2 ZE551ML - 06/02/2015 v4(old)
Allen Ngo

Chassis
85%
Keyboard
67 / 75 → 89%
Pointing Device
92%
Connectivity
46 / 60 → 77%
Weight
91%
Battery
92%
Display
85%
Games Performance
61 / 63 → 97%
Application Performance
54 / 70 → 77%
Temperature
93%
Noise
100%
Audio
59 / 91 → 65%
Camera
65%
Average
76%
85%
Smartphone - Weighted Average

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> Notebook / Laptop Reviews and News > Reviews > Archive of our own reviews > Asus ZenFone 2 Smartphone Review
Allen Ngo, 2015-05-25 (Update: 2015-06-21)
Allen Ngo
Allen Ngo - US Editor in Chief
After graduating with a B.S. in environmental hydrodynamics from the University of California, I studied reactor physics to become licensed by the U.S. NRC to operate nuclear reactors. There's a striking level of appreciation you gain for everyday consumer electronics after working with modern nuclear reactivity systems astonishingly powered by computers from the 80s. When I'm not managing day-to-day activities and US review articles on Notebookcheck, you can catch me following the eSports scene and the latest gaming news.