It looks like a machine that operates on ultrasonic frequency, though I'm wondering what kind of frequency it runs on, without having any kind of gel to contact it with the body. (Ultrasound is a form of Acoustical Energy)
An FYI...ultrasonic sound is defined as a frequency beyond the range of the human ear, about 30,000Hz, and it cannot penetrate anything through air, so it has to have a "medium", like the gel that you get slopped on before an ultrasound test.
Also, the ultrasound machines uses multiple vibration elements, and I wonder if this "Frequencer" uses the same method, or just one great big transducer.
Also, the other question would be the depth in which it becomes less effective.
IF, SAY, it is ultrasound, it should go all the way back to the rib cage, so that would mean a more effective "vibration" than the vest, however one thing that has not been proven is what side effects there are with ultrasound.
Ultrasound is still energy, and when the energy is absorbed, it transfers into heat. The question I'd have is what kind of effect there was with heat generated. Up to this point, Ultrasound tests has not had any detrimental effects, but then it wasn't used as a percussion machine, either.
On the other hand, if it's the same effect as the bass drum at a Rock Concert, it'd be worth the buy, since I thought the vibration from the bass drum was really penetrable...but then that's not ultrasound. I guess I got my "Pros" and "Cons" pretty much figured out! It does offer a 30 day money back guarantee!
But, it was a great discovery Prussian, regardless! (Thanks!)
(P.S. My favorite method of mucus clearance was getting thrown on the tatami mats! )