I think this depends if you are creating MType add many different places or only at this place. If you are creating MType at many places always having to switch for the dicsount type of have some other checks then this could be a code smell.
I would try to get the creation of MTypes in one single spot in your program maybe in the constructor of the MType itself or in some kind of factory method but having random parts of your program assign values could lead to somebody not knowing how the values should be and doing something wrong.
So the switch is good but maybe the switch needs to be moved more inside the creation part of your Type
