https://www.quartetapp.com/

This looks and sounds promising. Definitely a step up from BIAB, and arguably a bit less expensive if you go for all the audio packs for BIAB.

Main issue at the moment is that transposition effects the drums along with the pitched parts, ideally they should be independent... but small shifts should be usable.

Very nice LIVE playing, good song selection. I could probably get away with a nice cocktail jazz gig using only this...

Many of us have heard the Jamey Aebersold LP's, this brings the concept into the 21st century...

I’ve been using it for practice and even on a cocktail gig with a nice , in tune baby grand .
Of course it doesn’t have the flexibility of iReal Pro, but the LIVE playing, be it fairly pedestrian especially drum wise, has a nice steady feel that won’t get in the way.

I’m very happy with the purchase!

Did you buy all four packs for it?

Yes, and so far I’ve found all the jazz I would ever want.