I've got phats and they can be temperamental, to be honest thought it might be because I've been running them in the rain with a grind so light it's barely scratched the surface, that and the grind is dead.
They slip occasionally but as aforementioned, my set up is less than perfect.
A huge bonus for me is that they're completely silent with a 2bolt booster set up.
I'm going to give it a fresh grind tomorrow and then go off for a ride in the freezing, pissing rain.