I feel the issue is deeper than that.
We no longer buy products, we rent them, it's hard for consumer protection laws to catch up with that (even European).
Frequencies you don't hear - can't hurt you, or rather they cannot damage your hearing. Sure, submerging your head into an ultrasonic cleaning bath will irritate your skin, but the energy won't vibrate away your hearing abilities, if it had the potential to do that you'd hear it as a loud unpleasant sound.
Not to take away from the simplicity of use, of course, totally giving it a go. I think this is an awesome foot in the door for people who never considered developing extensions.