About 5 years ago, I had a 17 year old pony who underwent colic surgery. As part of his rehab, I was given a set of the bands. Narrelle Stubbs, who was then still at MSU where he was treated, also designed a core strengthening program for him. He came back better than he’d ever been. Since then, I have occasionally used the bands short-term with him if I wanted to up our game a bit more and I was pressed for time to put lots of miles on in the saddle. All with good results.
I have also used them to leg up another pony who had been a pasture puff for well over a year. They were also very effective for him. They are very easy to use.
The horses do get a workout, but I have not had them put up any protest to them. I have not had one become sore from their use. I find I just have to be careful not to ask too much at first. As mentioned up-thread, 5 - 10 minutes. Once I got to the point of 20 or so minutes, the horses seemed to have good strength and muscle memory and I went back to working without.
The only con I would say is cleaning the pad. I’m hesitant to throw it in the wash with the buckles, so I use a very thin pad under it just for the sake of keeping it clean. Has worked decently so far.
Yes, I would spend good money on the set based on my experiences.