I bought this to replace a very similar phone case (the outside of it had cracked in 25C-26C heat, I hope this one doesn't!). First thing to say is that the case I was sent was 1900mAh, not 2000mAh as described. I don't know if this is standard or due to a slightly unscrupulous third-party seller. I decided 100mAh wasn't a big enough difference to complain over or return the case.
This is a decent case that fits an iPhone 4/4S very well, and provides probably around 40% of a full charge for my phone. This doesn't compare well with other similar charging cases I've had in the past, but other people may get more as my phone is a couple of years old and the battery not quite as efficient as it once was. One minor problem is that although there is a hole around the camera, if you take photographs with the top half of the case on, you tend to have white bits around the corners of the photograph. This means you need to remove the top of the case when taking photographs, which isn't ideal but at the same time not too inconvenient. You are not provided with a plug, just the USB cable that plugs into the bottom of the case. You can then connect this to a computer, or the plug from an iPhone charger for mains charging. It takes a few hours to charge the case from empty to full.
All in all, not a bad item but there are better charging cases out there.