Probably more harm than good- you probably don’t want ultrasonic waves shaking your neurons around without a good reason. This sounds like a “kick a TV and it works again” sort of technology.
I can't find the link now, on mobile, but I found reference to using low frequency sound/light and that (anecdotally) individuals had tried this with their Alzheimer suffering relatives and had great success, like miraculous recovery of memory.
I wonder if there is a natural occupational exposure (CRT TV?) that could give evidence here, like if fewer people long-term exposed to low frequency sound/light get Alz?
Related: prenatal ultrasound could be significantly damaging, https://www.pnas.org/content/103/34/12903.full.
Extreme examples are chemotherapy, i.e. giving poison to cancer patients, and radiotherapy, i.e. irradiating them. The healthy cells can take it, the cancer cells not so much. Statistically.
Obviously, very big ethical issues arise when experimenting on people, but that's nothing new. Someone took radiotherapy first, before anyone was sure it was worth it to the individual.