I think it depends on the breed and how often they are socialized. If they don't have a lot of contact with people, it stands to reason they could become agressive towards people. If he is the only rooster you ordered, you shouldn't have a problem with him being too harsh with them. It is only a theory based off my experiences with the 9 roosters I've had.
Regardless, I bet you will have tons of fun. I'm debating on ordering from MyPetChicken this year, but it depends on the people who are ordering with me.
