new app "XXL Messages" - need coding advice

g.setFont('6x8:5x9') is slow, maybe

It shouldn't be - the call itself will be fast, and upscaling the built-in font should be reasonably quick

Bangle.on('touch', function (b, xy) { xxl.stop(); }); does not really work.

It should - maybe add some prints to the rendering function and see if it really is taking ages.

Must I undo the setWatch

Not with load(), no. You'd asked on another post about vars, but basically load() tears everything down so you don't have to worry.