Well what do you propose to do if zapping causes the parasites to go in unreachable areas of your body from zapping?
At least some medications can get systematic parasites. A big criticism on purely herbal protocols is that people report scattering and it seems like zapping could have the same issue.
If it could work all the more power to people benefitting from it, but to knock medication that may have strong effects on parasites, the same can be said about herbs and zappers if they don't work fully to eradicate the problem.
There could also be an idea to combine two or three of these methods but its up to the people treating themselves or working with a doctor, etc