Apple's 2014 iPhones have made a predictable dent in both the media and the high-end smartphone market, with the 'upsizing' of the handsets and the simultaneous release of iOS 8 grabbing much attention. However, even the larger of the two new handsets, the iPhone 6 Plus, only has a 5.5-inch screen, which hardly makes it a groundbreaker — Samsung's 5.7-inch Galaxy Note 3 came out a year ago, for example. Our review unit here, the iPhone 6, has a 4.7-inch screen — as seen, for example, in the late-2012 Google Nexus 4.

Three provided us with a 16GB iPhone 6, which is available on contract from £38 a month. The 4.7-inch handset is also available SIM-free from Apple for £539 (inc. VAT, £449.17 ex. VAT) with 16GB of internal storage, £619 (inc. VAT, £515.83 ex. VAT) with 64GB, or £699 (inc. VAT, £582.50 ex. VAT) with 128GB, in silver, gold or 'space grey'.

Design

The iPhone 6's look and feel is superb — this is the best-designed handset we've seen in a long time. Our silver review sample's white glass front looks superbly high quality and robust. It curves slightly into the edges of the phone, and while the join between the glass and the aluminium chassis is visible, it's probably as neat and smooth as it could be given the materials.

The phone's four corners are curved, as are the edges. The edges wrap around to the back, where the aluminium is interrupted by neatly fitted strips that allow the phone's antennas to function. The look of the back is reminscent of the HTC One M8.

The iPhone 6 is extremely slim, measuring just 6.9mm thick. Very few handsets break the 7mm barrier, so Apple's achievement in this respect is impressive. It's also very light at just 129g, and feels like a featherweight in the hand.

The iPhone's thinness doesn't compromise the buttons and connectors, which feel fine in everyday use. The power button is on the right edge, along with the nano-SIM card slot. The Lightning (charging and connection) port and speaker are on the bottom, while the volume controls and speaker mute toggle button are on the left. The top is clear.

There are several (small) elephants in the room, though. The metal-and-glass construction makes for a handset that can be quite slippery to hold — we nearly dropped it a couple of times when taking it from a pocket in haste to answer a call. Of course a case will rectify this (albeit at the cost of extra bulk and weight), as will acclimatising to the new handset generally.

The thin chassis has some consequences you might not like. For example, the camera lens surround protrudes from the back of the casing by about a millimetre, which rather breaks up the phone's otherwise very clean lines.

More significantly perhaps, Apple has only been able to squeeze an 1,810mAh (6.9Wh) battery into the iPhone 6. This may not keep you going beyond a day if you use power-hungry applications or games and are a frequent user of apps throughout the day. On the other hand, standby time is very good at 250 hours, and careful users may get a couple of days between charges. Having noted all that, the iPhone 6's battery life does seem to be slightly better than of the iPhone 5s.

Or final mini-elephant is that the iPhone 6 is rather taller than we'd like. Apple has always had a penchant for relatively large screen bezels at the top and bottom, and the 4.7-inch screen sits in a chassis that's 138.1mm tall. By contrast, Google's Nexus 5 fits a 5-inch screen into a 137.8mm-tall chassis, while the LG G3 has a 5.5-inch screen and is not much taller than the iPhone 6 at 146.3mm.

Apple refers to the iPhone 6's 4.7-inch, 1,136-by-640-pixel screen as Retina HD. Its resolution may be higher than the 4-inch iPhone 5s, but the pixel density of the two handsets is the same at 326ppi. The iPhone 6's extra pixels simply cater for the increased screen size. Contrary to pre-launch rumours, there's no ultra-hard sapphire glass protecting the screen, just industry-standard 'ion-strengthened' glass (Gorilla Glass being the best-known brand).

The increased screen size can accommodate six rows of application icons as standard. If you find this a little hard on the eye, you can opt for zoomed viewing instead. This reduces the amount of visible information to five rows of icons, as in the iPhone 5s. Apps will need to be updated to take account of the iPhone 6's increased screen resolution, so early adopters may find the handset switching in and out of the two resolutions automatically.

You can also pull the top of the screen down towards the middle with a double tap on the home button. This could help smaller-handed people work one-handed, although it does seem a little gimmicky on what is an average-sized phone screen in today's terms.

Touch ID fingerprint login is still present on the home button, of course, and is very well implemented. The setup process requires numerous presses of your chosen login finger pad onto the button, so that the iPhone can record its all-round pattern. We recorded our right thumb print: thereafter, touching the home button when working one handed resulted in efficient unlocking every single time.

There's no change in the resolution of the front (Facetime HD) and rear (iSight) cameras, with the former at 1.2 megapixels and the latter at 8 megapixels, just as with the iPhone 5s. But there have been some tweaks, including an improvement in autofocus speed (thanks to a new sensor with additional Focus Pixels), which we found impressively fast. Other new iSight camera features include 43-megapixel panoramas, a time-lapse video mode, 1,080p video at 60fps and slow-motion 720p video at up to 240fps. The Facetime HD camera, meanwhile, gets improved face detection, a burst mode and HDR video.

One new feature is notably missing from the iPhone 6's iSight camera: optical image stabilisation when shooting video. If that's important to you, you'll need to look at the bigger (and more expensive) iPhone 6 Plus.

Apple is keen to have a slice of the burgeoning wellness market, to which end the iPhone 6 has a built in barometer. This uses air pressure to estimate elevation — a vital piece of the puzzle of recording fitness information. There's also a new iOS 8 app, Health, that's designed to bring together data from a range of different sensors and fitness apps.

Apple's new Continuity features, including Handoff, will appeal to anyone using a Mac (running OS X Yosemite) or an iPad (running iOS 8) that's signed into the same iCloud account as their iPhone 6. Essentially you can take calls or SMS/MMS messages from your iPhone 6 on these wi-fi- or Bluetooth-connected devices, and also start a task — writing an email, for example — on one device and finish it on another. Apple's Pages, Numbers and Keynote apps all support this feature, and it will be available to third-party apps too. An added bonus for wi-fi-only iPad users is the ease with which you can set up an 'instant hotspot' on your iPhone 6.

NFC is now supported, but disappointingly it's currently redundant as far as UK users are concerned: it's configured solely for Apple Pay, which is only available in the US at present.

There's still no MicroSD card expansion, and the 16GB of internal storage on our review unit was reduced to 11.6GB by iOS 8 and Apple's suite of apps. You get 5GB of free online storage with your iCloud account, which you can upgrade to 20GB, 200GB or 1TB for a monthly fee (see Apple's website for prices).

Dual-band 802.11ac wi-fi is supported, along with Bluetooth 4.0 LE and LTE mobile broadband — now with expanded coverage of 20 frequency bands. The processor is a new 20nm dual-core Apple A8 SoC running at 1.4GHz. As with the iPhone 5s, the 64-bit main processor is accompanied by a motion coprocessor, in this case the new M8, that offloads processing relating to sensor data (accelerometer, compass, gyroscope and barometer) for improved power efficiency. The iPhone 6, like its predecessor, comes with 1GB of RAM.

A feature of the A8 processor is hardware support for Apple's new Metal graphics technology, introduced with iOS 8. Designed primarily for games, but also any graphics-heavy app, Metal includes an API, precompiled shaders and multi-threading support.

Performance & battery life

As noted above, the iPhone 6 is powered by the 20nm, 1.4GHz A8 SoC, which Apple claims offers 25 percent better CPU performance, 50 percent better graphics performance and 50 percent better power efficiency than the 28nm, 1.3GHz A7 used in the iPhone 5s. To examine these claims, we ran a number of benchmarks on the iPhone 5s and 6 — and also, for comparison, on a high-end Android phone, Samsung's Galaxy S5.

The iPhone 6 delivers 11.6 percent better performance than the iPhone 5s on the Sunspider 1.0.2 JavaScript browser test, with the Galaxy S5 (tested using its native browser) separating the two iPhones:

Under the Geekbench 3 CPU test, the Galaxy S5 beats both iPhones on multi-core performance, while the iPhone 6 delivers a 13.9 percent better score than the iPhone 5s. The 64-bit iPhones turn the tables on the Galaxy S5 when it comes to single-core performance, where the iPhone 6 beats the iPhone 5s by 15.9 percent:

The AnTuTu benchmark examines several subsystems (UX, RAM, CPU, GPU and I/O). The iPhone 6 comes out on top here, delivering 16.9 percent better performance than the iPhone 5s:

It's unwise to read too much into mobile benchmarks, but these results do indicate that the A8-powered iPhone 6 delivers an incremental speed improvement over the A7-powered iPhone 5s, and that it can more than hold its own against high-end Android handsets in terms of performance.

What about battery life? Apple claims 14 hours of talk time, 250h on standby, 11h of internet use or video playback on wi-fi and 40h of audio playback from the iPhone 6's 1,180mAh/6.9Wh battery. By contrast, the claimed times for the iPhone 5s, with its 1,560mAh/5.9Wh battery, are 10h talk, 250h standby, 10h wi-fi internet or video playback and 40h audio playback. That's a 17 percent increase in battery capacity, a 14 percent increase in talk time and a 40 percent increase in wi-fi internet time.

If the iPhone 6's battery life isn't enough for you, you'll need to consider the bigger iPhone 6 Plus, which packs a 2,915mAh/11.1Wh battery and delivers claimed times of 24h talk, 384h standby, 12h wi-fi internet, 14h video playback and 80h audio playback. The 6 Plus runs on the same A8/M8 platform as the iPhone 6, but is physically larger and heavier to accommodate the 5.5-inch screen.

Conclusion

The iPhone 6 and iOS 8 are both similar to earlier incarnations, but the new handset and the new mobile OS offer plenty of new functionality too. Taken together they make the iPhone 6 a great example of how to maintain the familiarity of previous releases while delivering significant enhancements (and iOS 8 adds many more new features than we've covered here). Overall there's enough on offer to entice existing iPhone owners to invest in an upgrade, and plenty to attract converts to the iPhone ecosystem.