Imo zappers don't work for large parasites. To get the big ones out you have to use the big guns, either strong meds, high raw high enzyme foods, strong herbs at 10x normal dose, high dose diatomaceous earth, or a complete multifaceted gut cleansing program. I don't even think they work at all for any visible parasites, maybe they work for minor league bacterias. (cue the entrance of parazapper salesman underwhelmingingaire in 3,2,1)
This opinion is shared by virtually all other credible people on cz who have been through the process.
There are a few stragglers who disagree, one is a salesman and the other, well I'll leave you to draw your own conclusion.
The theory seems sound, but it doesn't bear out in reality with credible people who actually have used them.
The difference between zapping and things that actually work becomes profound once you have already done a lot of deep cleansing and are attuned to the inner workings. If you are a beginner you might be tempted to think something is happening when you can feel the slight electric tingle at certain frequencies.
P L A C E B O
This is not to be confused with higher voltage plasma devices which I have no experience with and neither is the parazapper a rife machince since it is not a plasma device.