I wanted a battery charger, mainly to supply batteries for a power-guzzling Magic Mouse, and chose this one because of its features and the Duracell name. It comes with four AA low self-discharge nickel-metal hydride (LSD NiMH) batteries, a relatively new kind of battery which reduces self-discharge, extending shelf life between charges.
The unit can charge batteries singly, and can charge a combination of AAs and AAAs. It also has a USB port that can be used to charge a device from the mains or from a set of charged batteries. It's touted as a "mobile" charger due to its compactness, but here is the one reason why it just misses out on being 5 stars: the mains plug attaches to the charger itself, meaning that you need a lot of space around the socket in order to plug it in. Thankfully, the space needed is upwards rather than downwards, but generally I find that a plug on the end of a cable is easier to use in most situations, even if you lose a tiny bit of "portability".
If looking to buy a set of AAAs to go with the charger I'd recommend the "Stay Charged" Duracells. These are the rebranded equivalents of the "Active Charges" that come with the unit, and feature the same LSD NiMH technology mentioned earlier.
Amazon are currently selling these units for £ - an absolute steal at anywhere near this price.