The effect of a zapper on a jar of water has no relevance for what actually happens in the human body. Salt will also kill bacteria in a jar of water, does that mean eating salt will cure you of MRSA? Of course not.
Don't get me wrong, I am a zapper advocate. I just don't think they're as 100% safe as claimed, judging from my own experience with them. They have to be used just like any medicine or drug - with respect for proper and safe dosing.
I have used various zappers, like the Z4ex from ebay, but I've also just zapped directly from a simple 9v battery like Hulda described in her All Diseases book. All of them triggered the negative side-effect on my autoimmune disease if I used them 1) at low Hz frequencies (anything below 5000ish, though 15-100 hz were the absolute worst when it comes to pain) and 2) for longer than 10 minutes. As long as I didn't use it for too long, the zapper actually gave me immense relief though.
I have never used a ParaZapper. I've heard good things about your products. But they're too expensive for my budget. When I was at my sickest, I couldn't work because of how awful I felt all the time, and so I had no income, and no way to afford your product. I had to rely on cheaper solutions, like the battery zapping.
I'm glad to see you provide that disclaimer though. At least one zapper manufacturer has a conscience then.