You are spot on!!! It will likely be somewhat painful to those who need it the most. At least at first.
I had the Graston technique done on my left ankle for some extreme scarring after three reconstructive surgeries. It hurt so bad and the PT had to go so light with the tool that I could barely feel it at first or I would cry with pain. Eventually, the PT could get in deeper and it made a HUGE difference to my recovery and mobility. I would say that if your horses are very negative to it at first, they probably need it the most. Just be patient, go light for a while. Add pressure gradually. This tool has made a big difference with all of my horses. Pledge to give it six months.
One of my young horses was abused and flipped by a colt starter. When I found out about it and he came home, all of his muscles were spasming. It has taken a year and a half (using pharmaceuticals–robaxin–chiropractic, bemer, massage and now Perfect Prep) for him to recover to the point where he is moving again like he did before he went to be started. With this guy, he danced in the cross ties the entire time I was using the PP at first. Now, he sometimes dances when I do the first 1/4 of his body and then he relaxas and drops his head. So we are still working toward complete recovery (but very close). You have to be patient. My horse that is retired and has no issues, stands still for the PP and goes to sleep. My 3 year old that has just come back from the colt starter reacts negatively when the back half of his body is being PP’d. I figure he needs it the most there, but less pressure. This doesn’t replace the Bemer. I do the Bemer after.
If your horse has tight or spasming muscles, using robaxin and PP together seems to be a good combo to get them recovered faster without as much of a pain response.