I have a homemade zapper (someone made for me). I can't say I've ever noticed much difference but maybe I haven't used it consistently enough. My sister gets a lot of sore throats, she says that zapping with her homemade zapper usually kills the sore throat. There was a woman who used to post regularly called Paint Lady whose 6 year old daughter passed a bunch of worms the first time she used their homemade zapper.
I'm not convinced about zapping but I do it anyway!!