Well like Rodja had stated, on paper this may not be the missing link you're looking for - but you can't argue with the fact that many of the best MMA fighters past and present have utelized this in their training. wanderlei silva is the first person I ever saw use this method, he used a snokel and a nose clamp - now you see many fighters using the gas-mask version which probably works better and has different levels of filters to either lessen or increase the resistance. Bas Rutten was another advocate of the low-oxygen training and he even sells his own version.
Maybe this won't affect your number of red blood cells/level of oxygen utelization as well as the vendors would argue, but this can definitely help you get used to training well out of your comfort zone. Basically this is good (in my opinion) for getting you used to pushing past the point of perceived exhaustion, or getting you used to breathing with your opponents glove/arm/head/body over your mouth.
Basically what I'm saying is this may be a more useful tool for your mind than your body.