If you’ve got some spare cash burning a hole in your pocket and you can’t decide whether you want a new phone or a tablet, the Asus Padfone 2 might come to your rescue. It’s both. The phone is a fully fledged handset, self-contained and able to work on its own – in all the ways you expect a high end Android phone to.

But when you fancy a 10.1-inch tablet instead, you have one of those as well. The phone slots into the back of a tablet shell and gives this big screen and battery a heart.

The combination price of £599 is high enough to intially take some of the gloss off the product – you might have been hoping more for a two-for-the-price-of-one deal – and it might be more than you’d ever have expected to spend on a phone.

But if you are in the market for both a phone and a tablet, the price combination is attractive. Asus has married the two elements such that the combination offers a couple of distinct advantages too – most notably when it comes to power management.

One thing to be aware of right from the start is that the tablet doesn’t do anything on its own. It has no internals, as such, and it needs the phone to be slotted in before it will even switch on.

The tablet then uses the phone’s 13 megapixel camera (hampered down to 5.5 megapixels) and headset slot, the phone’s Bluetooth, GPS, Wi-Fi and 4G connections, and, of course, its processor and memory. The small phone screen, too, transforms into a large tablet one.

The layout of apps and widgets on phone and tablet are managed separately so you can personalize things as if they were two separate devices, but when you download apps and other data you do so to the handset as the tablet has no storage of its own.

Some apps can be set to automatically switch between devices when you dock and undock so it is always optimised for the screen size you are using.

That’s not the bed of roses you might think, because memory is limited. There’s no memory expansion on either the phone or the tablet, and the 32GB on the handset is down to just over 25GB of actual free space out of the box.

This is one of the downsides to the two in one approach, since the likelihood is you’ll use a phone and tablet in different ways – the phone for music; the tablet for movies, for example – and you may need to compromise between them.

In design terms Asus has done its usual slick job. The tablet is a bit of a block, but it has a nicely rubbery back and gently curved edges.

The handset has the optical illusion of being tapered thanks to a metal strip along the long edges that is thinner at the bottom than the top. The phone feels solid in the hand and its build quality is good.

The docking mechanism is secure and easy to operate – you just push the handset into the slot till it will go no further, and it slides out easily too. The switch from phone to tablet mode happens automatically, and almost seamlessly.

Specs

The phone’s specs are very good, matching leading devices like the Nexus 4. It is powered by a 1.5GHz quad core processor with 2GB of RAM in support, and it zips along. Its 4.7 inch screen, with 1,280 x 720 pixels looks great.

The phone runs Android 4.1. It isn’t vanilla Android, but the skin is light and subtle and the tweaks, mostly revolving around the format switching, feel necessary rather than bloat.

The tablet is slightly less impressive. The 1,280 x 800 pixels on offer are barely any more than you get with the phone, but stretched across an extra five inches of screen. The drop in relative resolution is noticeable, taking the device from high-end phone to mid-ranage tablet.

To help things somewhat Asus has implemented a special ‘outdoor’ brightness mode that racks up the brightness, but this pushes the battery hard. You can still take calls when the phone is docked – via speakerphone or a Bluetooth headset.

As well as providing the larger screen the tablet houses its own battery, and its use has been implemented very intelligently. You can set things up so that the tablet battery is used first so you have a well charged phone when you undock, and can use the tablet battery to charge the phone.

This really comes in handy if you find phone power running short during the day as there’s no need to hunt around for the mains. Because both devices have microUSB slots you can charge them both individually.

For some reason our review unit didn’t come with the slightly modified microUSB cables that Asus wants you to use, and our normal charge cables kept slipping out. That, the relatively low screen resolution of the tablet, and the lack of microSD storage on both tablet and phone could be ongoing issues, but in general we can’t help thinking that the Padfone 2 is a fantastic piece of kit.

It’s a great idea, and Asus is one of relatively few companies with the design and build chops to pull it off. It’s not an option if you ever think you might want to use the tablet and phone at the same time, but there’s undoubtedly lots to like.

Review written by Sandra Vogel