I ran through 150 rounds today, half of which were through the factory 6 round mad with the PG extension, and again not a single issue to speak of.
If your hands are medium sized you'll more than likely get the base of your thumb or webbing between it and your hand roughed up by the corner of the back of the frame seen here:
My last trip that saw 200+rounds fired left a bloody spot where the red rectangle is, and it's calloused up enough now not to bother me.
Note this is with some extended shooting. I don't use the PM9 as a target pistol, but since it had a malfunction at the range on its first trip I want to run as much ammo through it as possible to know that the problem is gone.
300 rounds later it sure seems to be a fine shooting pistol, made more enjoyable by the Pearce Grip.