I recently started using the jam or backing tracks function of this website and having been using the site for just under a year I really like it. I have left gutar fundementals 1 and 2 (for now) and music on to my first love the Blues and although the Jam backing tracks were meant for guitar I have been playing Blues harp (harmonica) for 36 years and find them very very usefull for blues harp as well. With each track it links to the lesson for it and that is awesome my guitar playing has improved dramitcaly since use the backing tracks provided on this site thanks to Guitar works.
And yes you can serve two masters. from the movie Crossroads.