On the Z guard in MMA: I think the best use of it was Jeff Curran vs Scott Jorgenson, and even though Jeff did a good job of limiting the hits he took, he still took a beating from Z.
It all goes back to the basic mantra: all the way in or all the way out, 'cause hanging out in the middle will get your ass beat up. Z simply leaves too much base, too much power and too many tools free.