TomTom is the market leader in portable navigation, and to a large degree its success in this area can be attributed to the popular ONE unit. Featuring an ultra-compact design that slips into your pocket for easy portability, an all-new EasyPort mount and exclusive TomTom functions like Map Share and the TomTom HOME service, the latest ONE improves on earlier editions.

It's hard to believe, but each incarnation of the ONE has been smaller than the last. The new edition is one of the smallest portable GPS units on the market. It fits snugly into even the smallest of shirt pockets. Its portable design is ideal for those who have multiple vehicles.

New to this unit is what TomTom has dubbed the EasyPort mount. This window mount can be left attached to the unit and folded flat after use, meaning the ONE is easy to pocket or store with its mount attached. The convenient circular lock means it's quick and easy to mount on your car window, and the well-crafted design allows easy titling in multiple directions.

The ONE interface is largely similar to previous models, so it remains easy to use thanks to clearly labelled and colourful icons. Our only complaint is changing settings — after adjusting certain preferences and saving them the screen goes back to the map display, so you have to navigate all the way through the menu again should you wish to alter any other options.

The ONE filters street names by suburbs, narrowing down your search results to a manageable number. The general navigational experience remains superb, with highly detailed maps, clear voice instructions and quick rerouting times. The ONE is also excellent at obtaining and maintaining a clear GPS signal, even with an obscured view of the sky. We found in most instances it took less than 30 seconds to get up and running after switching the unit on.

Most of the ONE's operations can be accessed via the main menu, which is split into two pages. From here you simply tap the 'Navigate To...' button. You can narrow down your search when looking for a specific address, as the ONE allows you to navigate to a city centre, specific street and house numbers, crossing or intersection, and postcodes.

The maps are very detailed and can be zoomed in and out easily using the '+' and '-' buttons. You can also view remaining time, remaining distance, arrival time, current time, street name and speed — these can all be turned on and off in the preferences menu. You can choose to have the status bar either horizontally or vertically, though the vertical setting is better suited to a GPS unit with a larger display. If you happen to miss the last voice instruction, you can tap the left-hand side of the status bar at the bottom of the screen to repeat it.

The ONE supports TomTom's new Map Share feature. In addition to corrections and improvements to the maps being uploaded every month by other TomTom users, Map Share allows you to make adjustments to maps through the unit itself. Users can add their own POIs, update road changes, edit phone numbers and add new streets. You can then share this information with other TomTom users by uploading the changes via the included TomTom HOME software.

TomTom's 'Help Me' safety feature is also included. This displays information and allows you to navigate (either by car or on foot) to a multitude of services including police stations, hospitals, mechanics, public transport and pharmacies. It even includes first aid, traffic regulation, and repair and maintenance information. In addition, the ONE comes preloaded with fixed speed and red-light camera warnings.

Battery life is rated at up to three hours. TomTom disappointingly doesn't include an AC charger in the sales package, so you'll have to charge the unit via the USB cable or cigarette lighter adapter.