I've used it to get wax residue out of cracks and seams. It works fairly well. I've never used it on the paint itself, though. I would reccomend a differnet product for that.
Brushes don't scratch, it is the crap that gets caught in them. Washmitts pull the stuff up and away from the surface. Brushes drag the stuff over the surface. Doen't matter if the bristles won't scratch, stuff in the brush will.