My opinion is that Parazapper brings up some very valid points. As a small analogy, I take a lot of vitamin C and am quite sure of its benefits at certain doses and I tell people this. They then later tell me "oh I tried vitamin C but it didn't do anything". Most times it's because they didn't take enough or didn't take it in the right way but it's hard to convince them of this and then they ignore what could be a very good thing for them. I find this frustrating to watch.
Parazapper is simply giving out what he thinks is important information. I really believe he gives this info out because he wants zappers to be known for their benefits and wants them to work. My first question to this forum was answered by Parazapper - he told me how to improve my zapper without once trying to get me to buy his.
I don't think I've heard him 'insult' or disparage the ZP zapper - he's just always voiced concerns that it may not be as good as it can be. People sometimes take this to mean that he wants to ruin them and just sell his zappers. I think people love the idea that the ZP zapper folks want to make zappers available to everyone for a next to nothing price and so they don't want people to say those zappers aren't good. It IS very good and nice of ZP to do this, but it doesn't mean that Parazappers comments are supposed to be negative, just informative.