aaron33- There are different sizes of BHBs, from toothbrush to paintbrush to about a foot long. I'd say we're discussing the latter. The paintbrush size ones are great for nooks and crannies though.
I've used BHBs for years and I still do *for some things* now that I'm all obsessive about my wash technique. They work *VERY* well in conjunction with a foamgun on really dirty vehicles due to their free-rinsing nature.
The handles don't cause any damage as long as you don't do something so careless that, well, you won't do anything like that so don't worry about it
BUT if you just use them the "normal" way, wiping them across the panels, you'll get marring from the dirt that gets trapped between the bristles and the paint. Probably not much worse than you'd get from using a mitt the "normal" way.
These days I *NEVER* press so hard as to be using the sides of the bristles

You'll grind the contamination into the paint and cause marring. I try to use so little pressure that I barely flex the bristles at all. Of course you gotta use a slick LSP (so dirt doesn't stick much) and you might have to pre-soak to loosen the dirt too.
The real ticket with a BHB is to blast sudsy soap through the bristles with a foamgun while gently rocking the brush against the panel. So gently that you just touch the tips of the bristles against the paint. This knocks the dirt loose from the paint so the foamgun's output can rinse it away. And since you're not wiping in broad arcs, even if you *do* get marring from the dirt getting pressed against the paint, the scratches will be maybe 1/8" long, which most people won't even see without magnification.