>- either EVERY zapper works, either NONE zapper works
I have to disagree, most zappers work but not all. Some of the worst ones that I have seen are more expensive. I service zappers and have seen some pure junk sold for well over $100. The only cheap zapper that I have been really impressed with is the $10 zapper from tendollarzappers.com. It is well designed and well built, but warning! It is limited compared to some more expensive zappers.
>- only if you are convinced it is working
This can be good advice if a person does not have serious issues and if they do not need fast results.
I have seen time and again where cheap zappers will beat colds and flu but fail in worse situations.