I've been looking for an emergency charging solution for my iPhone 4 for quite a while now. My main requirement was for it to be portable enough to have with me most, if not all of the time. What good is an emergency charging solution if it's not with you in an emergency?
When I saw that it was advertised as being small enough to fit on a keyring coupled with the Black Friday price drop, I quickly jumped at the purchase. The quality and build of the product is good - it has a nice rubberized texture to it. I have only used it to charge my phone a couple of times and each time it gives approximately a 30% charge to my phone before running out of juice. However, in my trials, I haven't charged it from a dead iPhone battery. I'm happy with the 30% as I expected as much after reading other reviews. My only issue is that it's not quite as small as I was expecting, but it's not a dealbreaker. I tend to keep lots of items on my keyring - usb drives, car keys, but this is definitely the biggest item on it.
If you're looking for an emergency charging solution, not something that will keep you powered on a backpacking trip through Europe, and looks are important to you, this is your product.