One the one hand: I prefer NOT using a used brush. On the other, every member of the family washes their body and hands with the same bar of soap...err..except SWMBO, who has separate bottles of product that need applied in some specific order so that they give maximimum beautifying, moisturizing, and youthifying effects....hmm..I don't know. Tough call.
I guess I'd err on the cautious side and buy him a cheapie. I've used a cheapie brush for a good long while now, and can't see any reason to need another. You might buy him the only brush he'll need this decade. That's a gift with longevity.