The water/meth injection tank holds a 1/2 quart of liquid and as far as how long that lasts would depend on how heavy handed you are with the throttle. You can set the controller to deliver the mix at a boost level that you select, usually around 8 pounds. Normal riding getting into some boost now and then, you would probably refill every other time you fill the gas tank. If you are a madman, it might be every time. Initially you really need to ride around and keep checking the first few times out to get an idea of how much you are in the habit of boosting your bike. The good part is that you fill it with the water/methanol windshield washer mix you get at the local auto store for $1.50/gallon, or less sometimes. As far as "fail safe" boost control is concerned, I have never used something like that. For me, the best fail safe is having the bike professionally dyno tuned. A good tuner will make sure your afr and timing are in a safe range, and there are ways to be conservative about this and still have a hard running, reliable and great turbo bike. I think any type of electronics that may shut off a fuel pump or cut boost mid-run might have a tendency to throw you over the bars in the extreme. These setups might work great on a car, but a bike is a different scenario. Again, I don't know for sure, having never used one or seen the necessity for one. You might want to consider a regular air/fuel gauge - at least you would be able to see something going too lean and back out of the throttle on your own. Again, a good tune is the key - timing and fuel.
