I don't think that anyone said it was a quack device. It is a modified type of TENS unit, and is registered as such. We know that TENS units have been helping people.
Its just the way the company does business that is in question. They do guarantee the product. IMHO They just sell it like a slippery used car salesman. They have a 'pitch' and a 'slip-slide' attitude in answering direct questions.
Their videos are, just so slightly, not too revealing.
The literature is all done by their PR dept,
and the medical reviews are on their payroll too.
A lot like the drug companies' way of doing things.
Just IMHO