When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am spraying 175 on a stock 99 C-5 (stock engine and fuel pump).
I changed to colder plugs, I dyno'ed the car and monitored the AFR during the testing. I monitored KR with a Predator, and pulled timing as needed.
The system is safe as you make it. As long as you follow the instructions, and it is installed correctly you should be OK. Stuff like the jetting (and don't accidently put the wrong jets in), the nitrous bottle pressure (using a heater and a pressure switch to maintain it for the pressure the system is rated at), use of a window switch, using a colder spark plug, turning off traction control when your spraying...
75-150 no problem as long as its installed right and used right.