>cleaning-intensity ultrasound could cause issues for humans?

Apart from it being loud as fuck? (They say it's ultrasonic, but there's some harmonic around 15,000 Hz that they all exhibit for some reason- both the bucket cleaners and the plaque picks at the dentist's office- and if you can still hear that frequency it is quite unpleasant.)

Most of the cleaning action of this thing is just mechanically being sprayed; I think they threw the ultrasonic cleaning action in just because they could. I'm sure it makes you feel cleaner though.