First, ignore most of the one star reviews. Many don't make sense, some don't apply to the book version, and a few are just plain whacko. This is an excellent instructive book--comb-bound to lay flat on a stand at that--to help any instrumentalist gain proficiency in not just soloing but improvising and, for those less experienced, understanding basic progressions in various genres. The easier, blues-based tracks are especially good for advanced novices who know basic pentatonic and blues-scale patterns, while the jazz patterns are challenging enough to keep those new to this genre interested. I did not use the thumb drive; instead I downloaded all the tracks to my computer, created a folder and copied them, and sent the folder to Google Drive, where then I open them up on my iPad blueoothed into a ElectroVoice PA monitor. It is a fun part of my (otherwise mundane) daily practice routine, both warming up and cooling down. Wish one could change track keys or tempos, but that's a minor complaint that does not affect this book's value.Highly recommended without reservation to all instrumentalists (those not in C will have to transpose accordingly) if you're serious about learning, improving, and refining your improv and theory skills. Sometimes to accelerate your learning process, you just have to JAM. And this book lets you do just that. Good job, HL.(PS one year later, I am amazed at how this book has improved my lead playing/timing/phrasing and rhythm comping. No other source has had this impact. The only ones I have not tackled are the 200bpm+ jazz bebop chordal melodies, but then I have little interest in being a chordal melody jazzer at this advanced stage of my life. If you're going to buy one backing tracks book, this is it, to where you can learn to fashion and hone your own licks and not feel compelled to copy someone else's.)