I just bought SKYYcamel's VYPR (for a really good price, thanks!) and I agree it's a great little
mod. The button is just about perfect - good audible and tactile click, and it works perfectly every time. It does not stick out very far and it's pretty stiff, so accidental pocket firings are nearly impossible.
If I have any complaint about it, it is that it could have been a bit thinner. There is about 2mm of extra space around the battery that isn't necessary. The spring keeps the battery from flopping around when the end cap is on, but it could have done without the gap at all.