I have the full StoneGuard kit on my car. I've had it for about 2 months now, and I'm quite happy with the results. Unless you get pretty close to the car and look carefully, you don't notice it at all. I also have the StoneGuard Light, which is a thicker foil that covers the lights. I think this extra protection will go a long way to keep the car looking good for a long time.
I don't remember the exact price, but I paid around $900 for the full kit and the light covers including installation. My advise is not to try installing it yourself, unless you really know what you're doing, since it seems pretty hard to get it right. And it looks ugly, if it isn't done right. Be careful in chosing the place that installs it. The experience with my installer was mixed. He didn't do a very good job initially, but went out of his way to fix it up. After I complained, he re-did the doors, and did some extra trimming in some areas.
Marc