The good: tracks are pretty high quality, and some have different styled versions, which is good. Also, you only have to pay for tracks you want, and you can preview portions first.
The bad: jazz coverage is weak. A few classics, like “All Of Me” we’re represented multiple times but a lot of the standards were missing. Also browsing for just the Jazz items was difficult, there is a Big Band playlist, but that had a lot of rock stuff in it. And Big Band is not the whole of Jazz by any means. Other than searching by name I couldn’t see any other way to find stuff, as the Jazz tunes seem to be buried, what’s there anyway, making it needle in a haystack time.
But it has a few gems, “In The Mood” Andrews Sisters style allows you to mute each of the three vocalists individually, and most of the instrumentals are pretty nice sounding, seems a cut above the Midi-player style of backing. For me it’s probably useful for a couple of tunes, and that’s about it for now. Maybe they’ll add more later.