The brushes are designed to break away from the rollers, so its unlikely you would notice as the person in the wash since the brush would come free and then be washed off / blown off throughout the wash.

Depending where you live underbody treatments may or may not be a good idea, if they HEAVILY salt the road it can get trapped above the liner and rust the car faster, bur admittedly I’ve only ever had second-hand cars with those treatments so maybe if done early in the car’s life and maintained its a non-issue