Zappers have their pros and cons, the best way to zap parasites is with herbs though internally... I once tried a product called the russian zapper which zaps you from the inside every 10 mins and kills tons of worms lol... thought I was going to die lol.
Be careful with these products and when using them remember your trying to get to a point where you rely 100% on nature... but if those aren't your goals then zap on and zap.
Internal zapper, wow. I've not seen those, and don't think I'm ready for something that intense. The one I use is external, low voltage and you don't really feel anything at the site.