I've had Commercial pilots do secondary stalls to see what it is and what not to do, but I've never found them troubling. Once or twice, we got the hard right in a power on stall, but only occasionally.

Commercial PTS is to recover at first indication of stall

Yeah, but I do try to have students recover from a full stall the first time they do it. Then I have them recover at first indication afterwards. It's nice to know what the airplane will do.

Well naturally

Things like that are one of the few things I enjoy about VFR maneuvers in flight training devices, Vmc demo gone wrong :). They might as well see what the outcome can be. After we do that i set them up for a low altitude Vmc roll, usually gets them the first time then they get smart about it.

there are too many factors to take into account to be able to say "this is how a power on stall should be done" all depends on the instructor and the airplane....i dont mind doing full power on stalls in my bellanca....it will stall and start to buffet but will never drop the nose, even has effective aileron input the whole way through the stall....wouldnt do that in a cutlass tho

My personal favorite is an engine kill at 80 kts in the F142 (PA-44 settings). Can't make it climb at all, even if you know it's coming.