It wouldnt be "bad" at all if and when installed porperly with the correct precautions taken. Nitrous is simply an oxidizer...the only thing it does it allow more oxygen in your combustion chamber (nitrous is about 33% oxygen while atmospheric air is just a tad over 20..like 22 or 23 %)...which allows more fuel to be burned, hence the additional power. Its not some explosive gas (its not flammable at all) that just goes in your engine and blows up. Yes...more stress it put on the engine at that time, but its the same stress that would be added by ANY power adder, may it be forced induction or otherwise. And as long as you take the right precautions and know your limits you will be fine.

What i mean by that is make sure your fuel system is up to date and working well. This doesnt mean you need to run out and replace or upgrade anything, just make sure your fuel filter isnt clogged to hell...and so on. The same goes for you ignition. Basically what im saying is on a healthy motor, nitrous will be just fine. However, i would advise that you change your plugs to ones that are "colder". Also, you want to make sure your clutch is healthy. Drag launces, and nitrous runs can easily kill a worn out stock clutch.

Your engine can easily take a 50 shot...65 would most likely be fine, and moving up to a 75 shot i would just take my time and "double-make-sure" everything is doing well. You can take your time working your way up to there as nitrous kits come with a variety of jets (for 35/50/65/75 hp shots).

One kit i look at is the Nitrous Express Kit #20923 (Import EFI). Its a QUALITY nitrous kit with a well-designed nozzel. Its what i ran both times on my mr2 (i went through 2 kits at 2 diff times)

Basically nitrous can be a hugely friendly power adder to those educated in what it is and how to use it properly, not to mentioned its Unbeatable power-cost factor. Its really the best bang for the buck out there.