I have two and they aren't very aggressive at all in my tank. Even my Red Zebra gets shut down by my Male Kenyi.
Just remember that whatever people might tell you, it could end up being the opposite. You could get a red top afra and he will be a complete terror, while a different red top afra would be calmer. Fish all have unique attitudes.
EDIT: Just to clarify, YES they are AGGRESSIVE fish. All cichlids are. My above post refers to level of aggression.
125g Cichlid tank