So, I just gave this stuff a more serious try. I did three full coats on the fenders, hood, mirror caps, headlights, and behind the wheels for a track day. It protected the paint well. It was very cold (for SoCal, 30F) so the coating was a bit brittle. I did see a few chips that went through the coating and damaged the paint.
I drove in the rain and it was fine. Even behind the wheels where the water splashes up. It did get a slightly milky color to it which went away when it dried.
Dry, it peeled off of my hood in one HUGE sheet. It is possible to wash the car and keep it on if you wash the car carefully. If there are exposed edges where it was previously torn, it will come up at those locations. Spraying it with a sprayer or pressure washer will peel it off. I peeled off the entire fenders with just a garden hose sprayer.
As for bits left behind in the cracks and crevices, most of that will spray off easily. I did have a few places that I either missed with the sprayer or wouldn't come off easily that I had to address manually.
You can't see it in the pic but the finish is uneven, has some roller marks, and looks a bit like truck bed liner.