Love these...they sound great! I also like having the different tempos.
I absolutely love having a studio license to these play-along tracks and using them in my studio! I send home CDs for students to use at home. I tell them to practice it on their own first (that's the learning phase), then play with the CD (that's the quiz phase), then at their lesson, we'll do it together with the teacher duet (which is different from their CD - that's the test!). I like that there are 4 tracks to each song in the book and that the tempos are so varied. Students are always able to play with the slow version, rather than it being too fast (like some I've seen). The fast version is great for students who are really motivated to get it. All in all, so glad I have these!
This is very useful to build up students' interest in feeling the beat!