I wouldn't do the bag trick that trainer did with the pony on a full sized unbroke horse.... They could bust a round pen in a big enough panic. It worked for the pony's circumstance well enough, I am glad I saw it... and it was the answer in her circumstance because she couldn't outstick her any other way. She said she had ridden out a lot of bucking horses and she just couldn't stay on that pony. I think because she is so small there is nothing to hang on to, your legs wrap around to nothing, and she is really quick. Bucking had always worked for her to ditch whatever was bugging her, and at least that one time, it didn't work. She did stop.
The question I have always had about doing that was How do they get it on the horse in the first place? Seems even if you hook it to the saddle before you saddle it would be difficult because of the rattleing.
Becky