I've just started using this, and I've yet to get to grips with how to use it properly. However, so far the response has been pretty good. I use it for a few minutes at the beginning or end of longer lessons for different reasons and with very different results. All beneficial.
I have an 8 year old who really likes it - partly because she doesn't have to work at reading. As her reading is good anyway, and as she's already had a long and intellectually fuelled day by the time she gets to me, I'm more than happy for her to create her own music alongside me. The results from this little one (completely lacking in self-conciousness), are at times bordering on stunning. She now asks for 'the book'.(She hasn't quite wrapped her tongue around the word 'improvisation'

). I can't wait to see how this one progresses .
I use it too, with a very tense adult student. (She also asks for it). This is the one time in the lesson, when she physically relaxes while playing. The musical results aren't as clear yet, but I'm very hopeful. I'm sure the sense of personal control and relaxation will eventually feed its way into all aspects of her playing.
I've also used it once with a teenager (very self conscious), who has some difficulty reading. The results weren't as good, but that was partly her reaction to something she was very unsure of. I will be trying it again with her. In fact, I anticipate rolling it out across all the piano students eventually. (Although I do need to do more work with it myself first).
I'd be interested to hear from others who are using it too.