Always only keep that rooster which is healthiest, friendliest, and well mannered with the hens, humans, and animals on your property.
You could leave him in the flock to see how he behaves. Also handle him and do a thorough conformation and health check. If he fails in any area, then imho, he is voted off the coop and I don't keep him.
You can then decide how well he blends in with the others in the bachelor pad.
Remember you don't need to keep a rooster as a matter of course. If he doesn't fit your flock needs, then he needs to head down the road to someone else or to the stew pot.
LofMc