Is Audiobus required?
Nope, Sqeech is all you need to make music. If you have Audiobus you can add third-part effects, looping, recording, etc.
App clips or crackles when playing
If your are clipping in Sqeech when playing with 4 or more fingers, turn "Pref > Sound > Touch Volume" down closer to 50% when playing with multiple effects/touches.
Where's the keyboard?
A piano looks like a piano because of the physical requirements of the strings, keys, and hammers. An electronic table-top synth is built around clumsy knobs and buttons because of the limitations of the physical hardware and circuitry.
A software synth doesn't have these limitations. Software can mold itself around the hand. It can understand the meaning in a gesture. A great synth can be hand-centric. That's what Sqeech is all about.