In the past few years I've seen more and more people wearing these depravation masks. They're wearing them while doing all forms of training where they look like Bane from Batman. The premise behind these masks is that by restricting the amount of air you get while training, the the harder your aerobic system has to work. The thought is this will improve aerobic capacity (your cardio). They've been popularized by "celebrity trainers" and UFC fighters wearing them in videos. The question however is, do they actually work or is it a waste of money?
By restricting the volume of air inhaled, these masks are meant to simulate training at high altitude where the air is thinner. The "thinner" air means you get less oxygen in each breath. This thinning of air at higher elevations causes the heart and breath rate to accelerate. This is an automatic response by the body to get the required amount of oxygen to the body's cells. While yes these masks do in fact make breathing harder they do not actually reduce the amount of oxygen inhaled (this has to do with air pressure).
Where you live will be the deciding factor on adaptation to altitude! An hour of cardio/training with something on your face making breathing harder will not. The reason for this is that the adaptation to altitude takes days and weeks of constant uninterrupted exposure to reduced air pressure. This forces the body to acclimate by producing extra red blood cells to carry more oxygen. That's what science tells us for altitude training. Also look at the posture of those training in these Bane masks. They're hunched over unable to expand their chest and maintain proper posture. This will directly affect the entire body's physiology creating added stress.
You want the training effects of altitude training? As already stated, that is determined by geography more than anything else. Think of places like Denver where NFL players with sickle cell anemia can't play games. Or East African nations where the most dominant distance runners come from. These locations have lower air pressure because they are at higher elevations! Plan an extended training camp in an elevated location before competition to reap some rewards!
Best thing to do is save your money and don't buy one and if you do have one, throw this gimmick away! Instead train intelligently! Lifting weights while deprived of air is foolish and highly dangerous as you are running the risk of a blackout. Results at the end of the day is what matter!