Just what exactly are people trying to rip off the metal surface with ultrasonic cleaning that can't be removed by more conventional means?
Protective oxide layer?
Protective metal plating?
The brass itself?
Cavitation (the 'abrasive agent' of ultrasonic cleaning) can do all this and more.
Trumpets have been around for a few thousand years and managed quite well without such brutal technology. I think it's probably a bit OTT myself.