Hi BluegrassPicker, I'm encouraged by your excitement for the app! I'm the primary developer for both iOS and Android BIAB.

If you import an SGU with a rendered M4A to the app, it does not require internet access to play the M4A audio instead of MIDI.

The apps have some limitations (for now):

MIDI Styles: Changing most song variables (key, chords, part markers) generally requires a local, offline regeneration. Tempo changes and instrument mute, volume, or patch change will apply in real time.

Real Styles (And any song with rendered M4A audio): Changing song variables, tempo, and track volumes need a regeneration on the server.

Realtime tempo control is an anticipated addition to both apps in 2026.