I have the venom 400 for my zx3, it doesn't raise the speed limiter. However, it does work with superchips. I have both and they work toghether great, you can feel the extra horsepower when it kicks in.
It does something very simple and not noticeable to the end user, if not knowlegeable enough to realize what it's doing.
It tricks the throttle into thinking the it is opened more than it realy is, therefore making you feel like you have more power with less throttle - Making the illusion that you have more overall power. When in all actuality all you are doing is going to WOT or close to it sooner than you should be.
But you know, spend your hard earned dough on whatever you think will make your car go supa fast.