I have had mares here who where PP trained and they where the hardest horses to work with. I will not take in anouther PP trained horse again. They will either have to be bred Shipped semen or not at all. They are pushy and ill tempered animals and I do now wish to work with that type of horse. There are to many good ones out there. The thing is it is not the horses falt.
I just started working for a reining horse trainer(I think this was in the late 90's??) There was a working student there as well. She was big into PP. We were both given colts to start. I spent as little time in the roundpen as possible. Even then I was a big fan of get an improvement and leave them alone, turn them back out. This gal would be in the roundpen Parrelli-ing the crap out her colts for long sessions. When it came down to it, her colts were crabby, ill tempered and looking for a way to "push" themselves on you. They were so sick of their jobs. Granted this may have been a user error, but I have noticed this with other PP users....the sessions are long and the horse is cranky.