go with nitrous express..
zex, nos, etc. rate their "shot" at the flywheel. NX rates it at the wheel. so in reality, with zex, you are probably getting 35-40 at the wheels, but with NX you are getting what the 'shot' is labeled: 50 whp. 50 shot of nitrous by NX is safe, and whats even better is that the import EFI kit is 35-50-75 shot adjustable. just go with NX