Hulda Clark 's book The Cure For All Diseases , describes the areas her positive-offset zapper can't reach (according to her) as being electrically shielded. However, she does say that she's seen the colon nearly sterilized in some cases by zapping. So I would consider your advice of replenishing the colon with probiotics, good advice for any zapper, even the $10 zapper which I think works just as well.
I do not doubt your sincerity or integrity, especially since you really do help provide zappers for humanitarian efforts. Good for you! I really do not think anyone is at all trying to scam with zappers, but it's too easy to believe half-baked suggestions because they seem plausable (or even obvious) without good evidence. Hulda Clark 's book is great in that she keeps an open mind about things she doesn't know. This idea is something that would be a very easy mistake to make, it SOUNDS good to me even. I am glad profit is not your only objective, getting good working zappers to more people should definately be the top priority for anyone in this business.
I simply am not convinced that there is a scientific reason for saying any zapper would work against organisms hiding within areas such as tooth fillings, gallstones, and the center of the colon due to any difference in voltage or frequency. They still have a higher physical resistance to electricity than the blood and lymph around them. Repetition and longer duration maybe helpful, maybe not. Consistency, yes that would help -- less reinfection that way. I'm not saying the claim is *definately* not true, just that I'm still skeptical and AFAIK it's not in the book. If you and/or another manufacturer have discovered something "new", it's certainly a great idea to use it to make better zappers. And if it really helps, I applaud you for it.
Looking forwards to that tricorder :D
[Edit: Slight correction to the above, fillings are actually way lower resistance than blood/lymph. Like a lightning rod, they shield the pathogens by channeling the electric current along a path that does not hit them.]