Awesome! It is awesome! The phone is definitely sexier and sleeker without it. With it, it is a fully functional beast of a machine. It changes some of the angles of the phone with the extended back. It makes for a very comfortable feeling in the hand for one handed use. It is bulkier. It has been totally worth it.
I had an issue at some point where it seemed the case back had some cracks at the edges...nothing had happened to it. I emailed them and they sent a replacement back.
Later...much later, I slipped in a wet stairwell and the phone dropped three flights. It landed on the back case. Yes, it broke the case map. Because of the battery weight, it landed on the back instead of the screen...at least I believe that is why. I purchased two replacement backs and considered the battery the reason my phone was saved.
I do not work for them. I used their extended battery for my Palm Pre and bought it right away for my 3d.
Dave