it doesn't really matter if your a beginner or not. zex is the easiest to set up for sure, but they are all about the same. i believe the zex kit is cheaper too but not sure. i have a couple buddies running the zex kit and they love em. just my .02
+1 That plate system looks cool, I'd bet its really easy to install and performs better than the usual jet sticking into the air inlet tube. If I didn't go with an inexpensive system and was willing to shell out a few more benjamins, that is the system I'd get.
I don't have first-hand experience with the Zex kit, but the consensus is that the NX kit is better. I've read nothing bad about the NX kits and read about a few less-than-great experiences with the Zex kits.
ZEX is nice because its a very clean easy install. but so is a NX plate kit. NX rates there power at the wheels too where as ZEX is at the flywheel. an NX 100 shot is about the equivalent of a 125 ZEX
Though I don't run nitrous (yet) my buddy runs NX and has had nothing but great experiences with it in all his cars. So much so that he became a distributor of it.