I installed a set on my XT 4-piston units (front 8" rotor) & I had a serious problem with glazing, they worked fine for a bit, then on a seriously steep section I could feel the pads hit the disc on cue, but no bite at all from the pads (dry conditions); I ran off trail & into the brush. Replaced with standard Shimano metallics & things back to normal (looked at the Aztecs & the glaze was very apparent on the outside edge of the pad). I may try them in the back where this may not be such an issue.
One thing though, I do have an issue with a pulse that raises its ugly head from my front 8" rotor....I don't have a clue what causes that. Time for a search unless someone can enlighten me. I don't think there are any bubbles in the system as power is good & the caliper is aligned properly.