Am looking to increase the horsepower on my Mini and am bouncing a couple of ideas in my head. Is any here using a nitrous oxide system on their minis or can give me an insight to this operation, also would it be easier to just use a water/meth kit taking into consideration cost, reliability, horsepower, etc?

 

Two very different animals from every aspect. You probably need to further define what your goals are and what you are willing to sacrifice to achieve those goals before proper suggestions can be offered.

 

Are you talking about using nitrous oxide to cool down the intercooler? There are cheaper alternatives.

 

For just all-out HP N2O is hard to beat for bang-for-the buck, I believe one of the M7 cars has a system installed and can give more technical details. The problem is N20 is illegal for use on the street and only really useful when drag racing, that and you'll have to pay to get the bottle refilled (or become a dentist).
Water/Met injections nice if you're tuned around it as it can prevent detonation. It won't really provide more HP so much as give you an additional safety net against horrific engine damage if your intercooler heatsoaks or something along those lines. Much more useful overall (when done properly) and cheap to refill.

 

The BIG advantage of water/meth for most people is that your car pulls hard like on a cold day, even on a hot day, even after many full throttle runs... it doesn't add "theoretical power" on the dyno... but it adds "real world power" in how much power the engine can deliver over and over and over and over again in real stop-and-go conditions, overcoming heat soak and other issues. You don't need to tune for it to get those advantages.

 

Blimey has it nailed, great explanation.