I was warned about these when going to school for Chrysler. I work for Cummins now (not wrenching now though), and they don't want us using them either, but they approve of the scotchbrite pads----which will put just as much garbage in the engine, but is easier on the deck surfaces doing it by hand vs a roloc on a die grinder. We have issues with protruding / dropped liners, so being carful on these engines is important.

The plastic bristle ones are approved though, but again, material gets flung all over, and yes, they can do damage to the surface too, albeit less IMO.

I am guilty of using them on decks, have for years, but I try very hard to keep it moving and not stay in one spot (kinda like leaving a belt sand in one spot on a piece of wood). Anyways, maybe its time to look at changing my methods when concerning deck surfaces.