To clear up any confusion, i own a 3Gs which was new on a Vodafone contract 20th January 2010, so to date, is loaded with the newest software updates etc. And this item works perfectly with it, there is no compatability problems( SEE UPDATE BELOW!).
Anyway it arrived very well packaged and inside the small box it comes in was a little instruction book explaining what to do etc.
It has a removeable rubber cover(stays on better than a hard plastic one) to protect the protruding connector when not plugged in, and in the bottom it has a connection the same as the iphone etc so this is where you plug in your cable to charge it up. it measures 63mm wide by 60mm high(not including the protruding connector) by 14mm thick. On the back it states, Capacity-1900mAh, Input 5v 800mA and Output 5v 500mA. It has a little button on the top right which when pressed will light up, up to 4 of the blue led's to show what state of charge it is in, the finish is nice, shiny black with a small chrome outlining just about visible in the pic.
For the price its a brilliant piece of kit, i've only just got mine today so cannot comment on usage but there's enough reviews saying how good it is. The back has nicely rounded edges whereas the front is pretty sharp/no blending on the edge. Does exactly what its supposed to, and for the £[] or so price is a wonderful bit of kit to own for your iphone. Delivery- it arrived on the tuesday(ordered weekend) so really impressive. All in all i'm very glad i bought it from Amazon!!!!! Recommended!
Ok update after using this a few times!!!!
I have been experiencing the 'accessory is not compatible with this iphone' sort of message, which means the iphone stops recieving a charge. Seems a random thing where it can charge from 5% up to 90% then suddenly stop accepting the charge, or, it can do it after 30seconds.
It just means you will need to unplug it for 5 seconds or so then reconnect it. That seems to sort it. Also, i get one full charge from say 10% up to 100% then maybe another 10% extra charge then its flat. it charges at 1% every 1min 35seconds. So 0-100% will be 100x 1min 35seconds, about... well its about the same as what it would charge up if plugged into the mains charger or pc.