to me it seems that if zapperplans wanted to use a 555 they would've in the first place and as analog kid stated a while back it is around the same price for a 555 as it is for a 4069!
I'm sure if you asked them they would say why they don't use a 555!
if they actually thought the 555 would be better they would probably use it!
I mean look: they provide a $10 zapper so that basicly everyone can afford a zapper!
otherwise they could sell a zapper for $50 if they wanted to and still get sales!
I think their is a reason they use a 4069 instead of a 555.