I like to keep bantam roos too.My Bantam roo gave his life for the girls when 2 neighborhood dogs got in my yard. I keep a Bantam with the big hens, he's not as loud, not agressive and does keep a watch out. Japanese Bantams rock.
Often they won’t damage the hens feathers at all and they’re perfectly able to keep watch and warn the flock.
Unfortunately two of my bantam roos died of unknown illness and right now I have a big Naked Neck and an Australorp.
If anything happens to those two I’ll probably replace them with bantam roosters.