One thing to note however is that when you transmute materia via Mutamix, you will not receive the same materia that you've added to the mix. For example, if I throw in a Piety Materia IV, Mutamix won't give me back a Piety IV as a finished materia.

It's worth keeping in mind if you were considering recycling the substat materia like Accuracy or Determination because they're most likely to be more valuable to sell on the marketboard.