I've seen videos of them before and I don't understand the concept. You can get plenty of back spin off of a Tanner tee you just have to teach hitters how to hyper-focus.
where DD trains, there are two hitting instructors who are recent DI grads that were both excellent hitters at different schools. they tried it and while one was killing the ball, the other couldn't hit well off of it.
so I guess different strokes for different folks takes on a whole new meaning