Safe and reliable, but not cheap. NX plate kit for the 2v 4.6. Usually go for around $600-$650.
They come with a wide open throttle switch, that is key!. The WOT switch will only allow the nitrous to activate at 100% full throttle.
You'll need a bottle pressure guage if it isn't included to make sure you are at the right level of PSI. $35~ if not included.
You should also invest in a window switch. Several companies make them, they can be found for around $120+... Summit Racing has one that may work, it retails for $40-$45 I think, but I'm not sure it's meant to work with the COP setup.
If you live in a cold place, a bottle heater is almost a must.
Remote opener is handy, but not needed.
Fuel pressure saftey switch is another safety option, but not NEEDED. It will cut the nitrous off if the fuel PSI falls below a certain amount.
It really costs alot to do it RIGHT. I would buy a kit lesser than NX, such as Dyno Tune as well though...
NX states that you CAN run a stock tune/timing with a 100 shot on their kits. Thats up to you if you want to risk that. AT LEAST put it on a dyno and check the A/F ratio while spraying if you felt comfortable with that. If not, add on the $ for a nitrous tune. YOU CANNOT RUN A PERFORMANCE TUNE WITH NITROUS! Added timing is a recipe for disaster.