The Mach X 2 is the Mach with a Pebax plate running through it. There is more foam than the Mach 6 carries, the rocker is more aggressive, and the plate snaps you off the toe rather than simply holding the shoe steady.
It is for the workout days when you want some of the help a race shoe gives without spending a race shoe's short life on a Tuesday. Tempo blocks, long intervals and a half you are genuinely pushing are where the geometry pays for itself.
It is not a recovery shoe. The rocker keeps nudging you forward whether you want to go or not, and at easy paces that gets tiring instead of helpful. It is not a marathon racer either, so treat it as a shoe that trains hard rather than one you race in.