The first Yotaphone was a phone like no other. From the front it looked like an ordinary Android handset, but on the back it had an always-on E-ink display that kept you up to date with notifications and appointments while using miniscule amounts of power. Unfortunately, the rear screen's lack of touch support made it maddeningly frustrating to use and it really dragged the handset down as a whole. It was a great idea that was poorly executed, but its successor, the Yotaphone 2, is everything the first handset should have been and more.

A lot's changed since we first saw the handset back in February , as you can now mirror the whole of Android 4.4 (with an upgrade to Android 5.0 Lollipop coming soon, according to Yota) on the back of the handset. This means you can make calls, send texts, use social media and effectively do everything you'd normally do on your phone all from the rear E-ink display. Even better, the rear screen now has full touch support, addressing the main complaint we had with the original Yotaphone.

While you won't want to use it for watching videos or playing games, this has huge implications for the phone's battery life, as E-ink displays consume much less energy than your typical LCD screen. The front screen already uses an AMOLED panel, which is more energy efficient than LCD, but Yota told us you can effectively read on the E-ink screen for five days straight on a single charge. This is immensely useful if you're low on battery and still need to use the phone for critical tasks such as navigation or making calls, as it enables you to stretch its 2,500mAh battery much further than usual.

You should still be able to get a day's use out of the Yotaphone 2 as an ordinary handset, though, as it managed 10 hours and 42 minutes in our continuous video playback test when we set the front screen's brightness to 170cd/m2. Admittedly, it's not the best battery score we've seen recently, as other flagship phones such as the HTC One (m8) , LG G3 and Motorola's 2nd Gen Moto X have all lasted around 13 hours in the same test, while the Samsung Galaxy S5 and Sony Xperia Z3 are both way out in front with over 17 hours.

That said, having the E-ink screen as a back-up display gives the Yotaphone 2 plenty of potential to outlast all of its main competitors. For instance, it took a full 24 hours to drain just 50 per cent of the phone's battery when we were using it over the weekend, and that involved using the front screen to take pictures, upload them to social networks, browse the web and periodically checking the rear screen for time and weather updates. Likewise, the YotaEnergy app can help get even more out of our battery by turning off key phone features whenever the battery falls below a set point. You can customise which features are turned off, too, disabling NFC, mobile data and Bluetooth, for instance, while keeping Wi-Fi, account synchronisation and haptic feedback enabled.

The E-ink screen isn't just a battery-saving exercise, though, as it does a lot more than simply mirror Android. Using the YotaHub app, you can configure up to four distinct home panels with all your favourite apps and widgets to take advantage of its always-on display. There are set templates to follow in terms of where you can place them, but there's a wide range to choose from, including clocks, calendars, weather forecasts, battery information, notifications and full-blown apps.

This is one of our favourite features on the Yotaphone 2, as you can simply put the phone face-down on a table and still be able to see the time, incoming notifications and any upcoming calendar appointments just by glancing down at the screen. It's a very similar idea to Motorola's 2nd Gen Moto X , which shows the time and up to three notification buttons when you either touch the screen or reach out for it, but the Yotaphone 2's always-on display is far more advanced, showing a lot more information that's both useful and practical. Both displays are made from Corning Gorilla Glass 3, too, to help minimise any accidental damage.

To access the other E-ink panel screens, all you need to do is swipe to the right or left like you would in Android. Admittedly, the E-ink display's slower sample rate means it will never feel quite as quick as swiping between home screens on the front display, but it still only takes about a second for the page to fully refresh. Likewise, the phone emits a small vibration with every successful swipe, providing a reassuring bit of haptic feedback to let you know you've done it correctly.

You don't need to worry about accidentally tapping other panels when you switch back to the front screen either, as the Yotaphone 2 will automatically lock the rear screen as soon as you turn it over. Its accelerometers are very quick to detect which way the phone is facing, although you'll have to make sure the phone is flat on the table before the front display will switch itself off. We particularly like how you can press the power button to unlock both the front and rear display screen, as we found swiping up from the bottom of the rear screen to unlock the phone was extremely temperamental.

Of course, you don't want all your calendar appointments and contacts on show when you're using the phone out and about, so Yota created the YotaCover to help keep your information private. This displays photos from a variety of different sources to form a make-shift screensaver and is also set up through the YotaHub app. It's a shame it doesn't happen automatically when you turn the phone over, but all you have to do to enable it is press the central onscreen home button on the rear screen.

One of the four panels can also be configured as a dedicated eReader using the phone's native YotaReader app. This only supports DRM-free eBooks, so Kindle users will be disappointed, but you can always mirror the Kindle app from the front screen instead if the vast majority of your library is tied to Amazon.

However, as the front screen's 5in, 1,920x1,080 resolution is much higher than the rear screen's 4.7, 960x540 resolution display, the fonts in the mirrored Kindle app don't scale quite as well as those in YotaReader. Not that you get much choice in the matter, as the YotaReader only has two different fonts to choose from.

This isn't great, but our biggest complaint comes from the E-ink screen's poor contrast. This leaves text looking very grey and sketchy, making it difficult to read on such a small screen. Even Amazon's cheapest Kindle has much blacker, crisper text than the Yotaphone 2, and when we compared both devices side by side, the difference was like chalk and cheese. This makes the phone a pretty poor eReader in this respect, and the native YotaReader needs a lot more work and optimisation options before it becomes a viable competitor to dedicated eReaders.

Even Amazon's basic Kindle model has a better E-ink screen than the Yotaphone 2

We certainly don't have any complaints about the front screen, though, as its 5in, Full HD AMOLED panel looks gorgeous. As we'd expect from an AMOLED display, it was displaying a full 100 per cent of the sRGB colour gamut, so colours were rich and vivid, and its black levels were a perfect 0.00cd/m2. The screen's contrast levels were also off the charts, providing the phone with excellent viewing angles and plenty of detail in our high contrast test images. Brightness was a little low at 268.93cd/m2, but we found this was still bright enough to use outside.

Performance is also right up there with the best smartphones from 2014. The quad-core 2.2GHz Snapdragon 800 processor might not be Qualcomm's latest high-end chipset, but Yota told us it deliberately chose the 800 so its heat dissipation wouldn't cause any distortion on the rear display. The 800's still a powerful chip, too, so it's not like you're missing out on raw processing power.

With a SunSpider JavaScript score of 830ms, the Yotaphone 2 is just as fast as both of Sony's latest Xperia Z3 phones and Motorola's 2nd Gen Moto X. Web browsing was also beautifully smooth when we were scrolling through The Guardian's desktop home page, and we saw no signs of judder whatsoever. Its stock version of Android 4.4 zips along nicely as well, making the Yotaphone 2 just as responsive as phones with more recent chipsets.

Graphics performance is equally impressive, as it maxed out both of our 3DMark Ice Storm and Ice Storm Extreme tests and scored a huge 15,592 (or 63.9fps) in Ice Storm Unlimited. Moreover, it managed 52.9fps on Ultra High quality settings in Epic Citadel, so it shouldn't have any trouble handling the latest games.

The rear 8-megapixel camera produced decent images, but it overexposed the sky quite heavily in our outdoor shots. There was plenty of detail on show, though, and colours looked rich and natural, if a little dull in the early evening sunshine. We wouldn't recommend using the camera's HDR mode, though, as this produced some truly bizarre images that almost looked like they're been turned into negatives in places. For instance, sections of cloud became solid grey lumps and lighter patches of cirrus clouds looked like they'd been infested with damp.

In Auto mode, the camera overexposed the sky but colours still looked reasonably warm and natural

However, when we switched to HDR mode, colours became very artificial and the lighting went completely off

Clouds became solid blocks of grey in HDR mode and the sky near the BT Tower looks as though it's been engrained with dirt or damp

The Yotaphone 2 has its shortcomings, but it's still a huge improvement on its predecessor with plenty of useful features. The full touch support makes the rear screen much easier to use, it has a potentially huge battery life and we're big fans of the always-on YotaPanels. However, we still feel there's more work to be done before it achieves its full potential, as its E-ink screen just isn't quite good enough to make it a viable alternative to a dedicated eReader. At £555 SIM-free, it's also very expensive, but this is to be expected given the fact it has two screens. There's plenty to like about the Yotaphone 2, but it just falls short of being a truly game-changing handset.

Hardware

Processor

Quad-core 2.2GHz Qualcomm Snapdragon 800

RAM

2GB

Screen size

5in (front), 4.7in (rear)

Screen resolution

1,920x1,080 (front), 960x540 (rear)

Screen type

AMOLED

Front camera

2.1-megapixel

Rear camera

8-megapixel

Flash

LED

GPS

Yes

Compass

Yes

Storage

32GB

Memory card slot (supplied)

None

Wi-Fi

802.11ac

Bluetooth

Bluetooth 4.0

NFC

Yes

Wireless data

3G, 4G

Size	145x69x8.95mm

Weight

145g

Features

Operating system

Android 4.4

Battery size

2,500mAh

Buying information

Warranty

One-year RTB

Price SIM-free (inc VAT)

£555

Price on contract (inc VAT)

N/A

Prepay price (inc VAT)

N/A

SIM-free supplier

www.yotaphone.com

Contract/prepay supplier

N/A

Details

www.yotaphone.com

Part code

Yotaphone 2