Multimammate mice (also known as soft african fur rats or natal rats etc...) are generally slightly bigger than fancy mice but need caging that is very secure. The chew through plastic and are also know for not being very sociable (although I would imagine there are exceptions to this rule). They do look appealing but are definately not fancy mice in respect of friendliness or environment concerns. They are normally bred by feeder breeders (due to the fact that they produce large litters) quickly.
I thought about keeping them a while back as pets, but need more convincing that they are not going to bite me everytime I put my hand in their cage! This seems to be why they are not kept in such numbers as pets as fancy mice are. The fancies docile nature makes it a better pet. But I suppose that comes from generations of breeding out their wild nature. Multis are generally still pretty crazy in temperament! At least, that`s what I`ve read and many people say when they own them as pets.