Being a little new in terms of posting here, I don't want to insert foot into mouth. I do not really agree though with the concept that mixing Mbuna and Haps is a bad idea. I think there should be included with that, depending on tank size.
In the years I've been breeding all three types, Haps, Mbuna, and Peacock, what I have found is for the most part, you'll find your Haps and Peacocks do not often dwell in the lower end of a tank, where Mbuna hang out. In terms of aggression, unless you have a very shallow tank, agression should not become an issue between these groups, even with larger Peacock males. Haps and Peacocks tend to be more open water types, indepenant of the rocky bottoms.
Tanks under 55 gallons though, will pose these problems. That's not to say either that a 55 gallon tank just opens the door. You still have to have respect towards what species you are trying to house togeather. You pick something hype like Auratus or Johanni, and they are as close to the South American Green Terror or Red Devil types in terms of temper, as you can get for Africans. These species simply don't play well with anyone.
I'd just like to offer that actually, it varies greatly between what species you are trying to mix, compared with the footprint. While that does seem common sense, I've seen too many people asking what more can they add in an already heavily stocked 40 gallon....I am no fan of the overstocking to reduce aggression either, but that's a seperate subject and thread. I also breed now, some Madagascars and Victorians. I'd be happy to offer input from time to time as needed.