Tuned right,proper timing,octane and fuel pressure,it is completely safe.Don't spray more than your piston ring end gaps are setup for(learned that the hard way
)And ALWAYS run a safety/scondary solenoid if you are planning to use a progressive controller.When I drove my Olds in high school I had a 175 shot on a 396 with Keith Black hyper pistons and sealed power plasma rings.I would literally go thru 2 or 3 10 lb bottles per weekend on the street using 93 octane pump gas.Did that for about a year straight,then cut back to 1-2 bottles a week for the next year and a half.Never one single problem.Used just a snap switch to activate,simple.I used good fuel filters and nitrous filters in front of my solenoids and cleaned them regularly.You'd be surprised trash what will come out of a nitrous bottle!!And USE A FUEL PRESSURE SAFETY SWITCH!!!It is safe and reliable if you keep it in good working order.Any setup is only as reliable as the man who tunes it.Don't cut corners and you'll be fine.Have fun!!!
P.S. Don't use it on the street,that was stupid...fun
...but stupid.