I had one with my boy for a while. I didn't like it, My guy really didn't need it, yet my trainer said that it would help ( and because I was at that point in life where I thought my trainer was ALWAYS right, and I trusted her completely ) I went along with it. At the time, I thought it was wonderful, my guy had a nice looking frame, he wasn't leaning on me, and my trainer said he went great. Long story short, he lost most of his topline, he started carrying tension and stress in his shoulders and neck, causeing extreme stiffness and eventual lameness ( my trainer at the time blamed all this on an ill fitting saddle and his 'bad' stifle, both of which were 100% fine). 2 years after leaving all that behind, we are finally getting back to where we were before, he is doing much better and I have never used that device again.
I don't want to blame the device, or my trainer for that matter, my fault entirely in that situation.
Anyway, just letting you know my experience with this device. Make sure you use it correctly.
" If the entire world was one big machine, I couldn't be an extra part. I had to be here for some reason." ~ Hugo Cabret