Yup, agree.
I'd buy new if it were me. That way your getting new, and not abused/neglected parts and equipment.
The new kits will come with a window switch, and a low fuel pressure shut off. Purge is needed for the wet kits, though I use one on my dry for the coolness factor. Bottle warmer, eh...only "really" needed if your bracket racing IMO. I don't have one, nor ever needed one. On a full bottle, on a warm day 900 PSI is not a problem. On a hot day I have seen as high as 1200 PSI. The minimum amount you want to have is 800 PSI in the bottle.
Other things I added were a nitrous pressure gauge in my pillar pod, and a remote bottle opener as well as a flip open "arming" switch to turn on the system. I added a small green LED light next to the gauge in the pillar so when the system was on, green means go.
I also built my own D.P.N.I. plate. (direct port nitrous injection). Its a 1" billet aluminum plate that sits under my GenV and gives a nice even healthy shot into each intake runner of the head. Before that, I used a phenolic throttle body spacer, taped that, and sprayed there.
I keep around a 60-70 horse power shot, as I use it as a inter cooler more than a horse power gain. That's just a good side effect.
~F~