No, this is not some post-apocalyptic face mask for when the sky turns grey with silt and ash from that volcano in Yellowstone (I think I have been watching too much Doomsday Preppers on National Geographic). It is actually a training tool for those of you trying to climb up high mountains, and trek at elevation.
The mask essentially does exactly what you think -- restricts the oxygen you breathe in. Why on Earth would you want to do this? Well besides looking fashionably questionable (and scary!), it conditions your lungs by strengthening your diaphragm, and increasing the surface area of those grape looking things called alveoli (this is where oxygen is pulled from the air you breath in, into your body).
It can be used during most exercise (caution is advised for beginners) and will allow you to build strength to summit that 14er without feeling faint, and trek up in the high Sierras without even noticing your elevation. Not only good for climbers, but for anyone who needs copious amounts of oxygen. This will increase blood flow and oxygen input for things such as running, cycling, rowing, etc.
Rogue Fitness $90