"Has anyone actually used this as a training aid?"
Just a couple million U.S. Soldiers and Marines for starters. I should point out that this is a training aid, not a substitute for training. It is understandable that a good rifleman may have problems with a handgun. Just as he had to learn to shoot the rifle, he now has a different tool he needs to learn how to use. The wheel is useful in telling what you are doing wrong but it doesn't teach you to shoot correctly. You need instruction on the basics followed by range time with a coach who will stand behind you and watch you shoot, then make corrections as needed.