[ne14t?]

To be honest there really isnt that many parts in a water/meth injection kit, the only thing that can really fail is the pump that moves the meth from the holding tank to the injector nozzle and of course human failure for not filling the holding tank up. In a sense it can be a band aid solution to your problem, I have seen people goto a water/meth injection kit because its cheaper then purchasing a installing a FMIC which is just stupid. In my opinion a water/meth injection kit is the way to go on any forced induction application, not only do you have a little more insurance against detonation but you also have the ease of running lower octane pump gas which is cheaper, not to mention each gas station has a different octane rating on there premium fuel. Look at it this way after filling up 15 times with regular your water/injection kit will pay for itself in comparison to filling up with premium. If you combine premium with water/meth your essentially ending up with something equivalent to 110+ octane race fuel opening up a huge window of possibilities on your tune/power output.

Edit: On a side note your MAP sensor will not detect if your water/meth kit is flowing, MAP = Manifold Absolute Pressure, its basically just there to get rid of your constricting airflow meter and serves the same purpose. Most kits now have a built in failsafe or some kind of alarm that will tell you if something is wrong with your injection system and as RG mentioned a lot of aftermarket EMS can be setup to change tunes if such a problem occurs. Check out the Snow Performance kits, especially there "safety box" it can tell your ECU to change tunes, trip a safety light and even disconnect your EBC and its not even proprietary to there water injection kits.