[Endoperez]

Master Matrixes surely are. They can be used to make a non-astral, non-blood mage lead a communion. Slave matrices are more expensive, but I could see using two if I have only very limited access to Astral mages otherwise, or would quickly lose them to Magic Duel or something. I wouldn't make too many of them, though, perhaps just enough to boost some mage 1 level for some important spell, so 2 slave matrices.