I just dabbled with it today ( I do have a day job which suffers greatly from my BIAB ownership as it is.) I scatted a few choruses to Rhythm Changes and "There will never be Another You."
The UserTrack DID actually work. My singing is reprehensible (and the playback stretched me from basso profundo to Munchkin territory,) but I DID make a UserTrack. Maybe this weekend, I'll try it with a horn and see what happens.
I'd be interested in a tad more documentation (limiting ranges etc.) I notice it doesn't transcribe, but that is no biggie. Don't want anyone stealing my licks THAT easily ....