Just got this and while I knew I should have charged it up first, I put it right on the phone (white iPhone 4S) which was at 40%. In one hour and ten minutes it had charged it to a full 100%. It looks great, has a bit of heft to it but doesn't add a lot of size to the phone - it still fits in my briefcase phone spot (which isn't that big). It offers better protection than the old case I had on it; it's plastic, but appears well made, and strong.
The design is nice: clean white but a dark grey side stripe all along the sides, top and bottom (I'd have preferred all white, but it does look nice and probably won't pick up dirt as easily). The lavender-blue lights at the bottom show the charge capacity and stand out against the dark grey. To check the status when it's not charging, you just press the button on the bottom of the Mophie and it lights up to show its current capacity.
It's easy to put on and remove - not a struggle like my regular plain case.
The sound is good - I could probably say better - than the iPhone 4S on its own. The little holes on the bottom front do seem to improve the quality of a phone call. I have only tried it twice but was pleased.
The photo area on the back has a black rim around it which is to prevent glare from the flash when taking a photo.
The cable to charge it (with your laptop via USB) is included. The instructions are in a little black book (the packaging is nicely done) and are in proper English, which is always a plus! They could have used bigger type than the 6pt they used in the booklet, but at least it's easy to understand.
I'd highly recommend it if you need a case and/or charger. At the rate it's going I expect the charge to last two days instead of the usual 8 hours, for me. I'll try to remember to update it when I know how long the charge actually does last.