"Poor Man's Fronts"! Can't go wrong there. lol
Never kept them, but they do have a rep of being quite nasty to others. Depending on what type of Mbuna you currently have, you may be able to get away with adding some.
I would say that in the end you would be lucky to keep more than one pair in the same tank. Start off with several juveniles, and let them pair off. With a good amount of rockwork on either side of the tank and a more open area in the middle, you may be able to get away with two pair. I can't say for sure as I've never kept them. But with two pair I don't think that your mbuna would fair very well.
You can do a nice Tanganyikan community in a 55. Have you thought about any other species that play nicer with others?