Yes its safe to spray and pray lol
I wont jump on the band wagon and jump your shit so to answer your question here is my experence with zex. I have ran up to 125hp with no problems however I only have 8,000 miles on my car. Before I ever ran my first shot I upgraded my plugs to the Brisk two degrees colder plugs and I always make sure I have 93octane fuel that doesn't have the ethonl adiditve (not sure if that plays a factor I just wanted to make sure it wasn't one) The bigger the shots of n2o I spray the more I up my octane level as well to make sure I dont PING and BOOM! I never spray under 3000 rpm either and I dont take my spray into the redline.
Here is my little rule book lol
75 shot 93 octane
100 shot vp100 street blaze fuel
125 shot Vp Motor sport 109
P.S. I am not saying this is how it has to be, this is just my way of making me feel better on the spray.