I've played 2 tournies in Viera with the Pro M and I thought the ball played well. One thing I will say, is that guys who couldn't even sniff the fence with ZN classic Ms down there were putting them out easily with the Pro M.
Let's face it, a .44 375 ball is too much with today's bats. USSSA needs to develop a ball that's soft, dead, and doesn't fluctuate much due to temperature changes.
Do I think there are noticeable differences in performance in Pro M batches? Yes. The first Pro Ms we used in Viera were hard and jumpy. Some of the ones I've seen this year seem noticeably mushier and not as lively.