"Is it dangerous?"

Nitrous Oxide is a tuning aid just like a turbo or supercharger but requires much less modification to your engine and is much more cost effective with higher power gains than most engine chips.

There are plenty of so called 'experts' and because not many people honestly know much about Nitrous Oxide (N²O), the 'experts' get away with telling you all sorts of pap.
Nitrous Oxide is not a flammable gas, it is an oxidising agent (i.e. it does not burn, but promotes the combustion of things that are flammable). The reason it works is the oxygen part of Nitrous Oxide allows your engine to burn more fuel.
N²O itself does not burn if you squirt it at a fire, in fact it will put most fires out due to the pressure it is stored at and the temperature drop it creates when vented from a bottle. Under the high pressures created in the engine, the oxygen seperates from the nitrogen allowing more fuel to be burnt. Nitrous contains a higher amount of oxygen than the same volume of ordinary air.

Highpower Nitrous Oxide bottles do not explode even if your car was on fire (you know which movie I'm talking about). Highpower bottles have a Safety Pressure Relief Valve (SPRV) which will release just enough nitrous gas (so you might hear a hiss), to keep the bottle pressure below a safe limit if the bottle is overheated. US systems however just have a pressure burst disc which will cost you a full bottle of gas and certainly make you jump if it bursts, but it's still not an explosion.

The only way N²O is dangerous is if you twat someone round the head with the bottle, which we do not recommend, or by inhaling it. Some people seem to think the gas has some sort properties that will get you high and make you run fast around the campsite (just dum people). Nitrous is inert and you will have just the same effect from inhaling nitrous as by holding your breath; lack of oxygen to the brain resulting in dizzyness, nausea or death by asphixiation (but this really depends how long you can hold your breath!!). It's used as a anaesthetic to balance the amount of oxygen reaching the brain to induce a controlled unconciousness and in ice cream production because it is a safe 'clean' gas. In fact, currently in the medical world it is used much less as an anaesthetic as the recovery rate with more modern injected methods are much faster with less side effects.