For casual use and for an occasional blast, the Zex kit is probably the most user friendly and easiest to use. It will, however, only spray up to a maximum of a 125hp shot. If you plan on using nitrous in larger quantities or for competition, I prefer the NX kit or the Edelbrock Performer RPM kit. Both offer a broad range of adjustability and value for the money involved. Keep in mind all the extra items needed to use nitrous with any reliability or consistency. Things like a bottle warmer, bottle blanket, purge valve, gauge and activation switch. You'll also want to think about a blow-down tube and hobbs switch for track legality and safety.