However, I have taken the advanced guitar course on there and I wasn't satisfied at all. Their definition and my definition of advanced guitar lessons differ. They would only give me a new lesson every week which I would blitz through in about 10 minutes.
The jazz piano program might be worthwhile, though. I believe that they do have demo's of certain weeks of different programs.
I have heard that PG Music's Jazz Piano Masterclass is fairly decent (have never tried it). They have a bunch of other piano programs as well.