I have the clear bra (3M, much thicker than the Stongard) on the Boxster. I have mixed opinions on it after two years. It looks good in some places, but not in others.
As far as what I don't like about the clear bra, here's the run down.
First, instead of the regular hood piece, I had a custom single sheet put on the hood so there would be no line across the middle where the plastic ends. This was wonderful until a few months ago when a huge rock hit the hood hard enough to cut through the plastic (9 mils thick) and take a scrape of the paint off. The plastic did its' job, but now there's an ugly, unfixable gouge in the plastic that catches dirt like crazy. Now I have to get that piece off.
That leads me to the biggest problem I have with the plastic. Where the edges end on really curvy surfaces (mirrors, bumper openings, etc.) it pulls up around the tight curves over time and the dirt loves it and won't let go. Also, any place where the edge of the plastic faces the front of the car collects dirt and gives you a dark line that's hard to get off because you don't want to pull off the adhesive that the dirt is stuck to.
On the bumper it's good. The guy who did mine used a kit that wraps around behind the bumper so it doesn't pull up around the outside edges, just on the air intakes.
If you get a kit and do it, make sure you use the directions and use heat to stretch it around the edges of the hood so the ends are covered and the only place you have an exposed edge is along the middle of the hood and behind the lights where the plastic ends. It looks much better on darker cars.
If I were to do it again, I'd get it on the bumper, the lights and the fenders behind the lights, but not on the hood or mirrors. 