What possible harm is there from at-home ultrasonic cavitation machine?

Hi, There are several 40k ultrasonic cavitation machines in market for $200 -$800. I am thinking to buy one, but i am not sure if their efficiency is comparable with what I can find in Doctors' offices. I believe if it is %50 less, still it is worth buying. Would you please let me know your thoughts about possible harm of at home RF/ultrasonic cavitation machines? Which tool parameter defines the tool performance that I have to be considered in choosing the model? Thank you