they are very comparable to damsels in size and demeanor.
they should only be kept with other malawi cichlids or with synodontis catfish, which are about the only other fish they'll ignore.
the great thing about them is that they LOVE to be packed together. this allows them to share the hate so that no one particular fish gets bullied to death. I have approximately 60 malawi cichlids in a 135 gallon.
aside from being mean to each other, they are GREAT 'people fish'. they'll come out and beg for food and they'll eat out of your hand (and they'll also bite your hand, but it doesn't hurt). several of mine will swim right into my hand and let me pick them up out of the water.
they are very easy to breed, but you have to be carefull of them hybridizing as this is frowned upon in most cichlid circles.
they are pretty hardy as long as you keep the right conditions and keep enough of them together (again, they love a lot of company from fellow malawi cichlids).
the PH should be 8.2 (just like saltwater) and Lake Malawi is slightly saline (barely noticeable really, but the cichlid salt really makes their colors shine). they eat mostly spirulina (again, similar to many saltwater fish) and brine/mysis shrimp.
they're fun fish and they're low maintenance. and most of them are fairly cheap.