I installed the kit on my old iPhone 4, as I'm too chicken to take any chances with my 4S, since I have the AppleCare+ on it.
So anyway, the install was tedious, and I took my time, so it took about an hour. It's a bit trickier in spots I didn't expect it to be. The way the wire has to sit on the tiny power pin and then taped down is really a poor way to make this work, but it does work.
My review is about the same as most peoples. Looks cool when on, but the fit is terrible. Gaps along the side and top, very thin and fragile feeling, the light is brighter on one side and not uniformed. It's a real down and dirty, ugly mod.
I put the phone in a Speck Gemshell to protect the fragile glass, and still show off the mod. It also covers the light gaps.
If the back case build quality was better, this would be great.