I have a pair that I use in lessons with students. I've had mixed results.
I think the problem has to do with the fulcrum pivot (the little button on the sticks). To work correctly you have to be teaching a strict German grip. Forget it if you are teaching French Grip. Also, at least around here, the mixed "American Grip" seems to be more common. That also will not work with this stick.
When I first got the sticks I tried them myself. It was challenging for me to stay in a strict German grip after playing with the American grip for so long. I missed using some of my other fingers for control.