I know the zappers hulda clark's son geoff sold were all junk. The manufacturer put all trash switches in them because geoff clark insisted on saving 2 pennies over using a quality switch. They lost all their business selling zappers and everyone I sold one too they all quit within the first year and within the next year I dumped everything Clark and have never sold their junk since.
Zappers designed on the same theory work, but I don't sell any or promote their use. I would use one on a dying or desparate person, but would prefer the very expensive Rife type machine over the cheap zapper spin offs. I like the rife ray tube machines that you just stand within 12 feet of and are all computerized, you just use the computer and pick out what treatment you desire and it does the rest.
Otherwise I only promote one electronic gadget, the russian pill zappers, they are the greatest advancement in electronics ever designed and been around as long as I have. They are not available in the usa, but the medical grade zappers are produced in the usa and kept secret from american doctors.