If you are marathon runner or trying to adapt to training at altitude ( ie. Denver, Colorado), this makes sense.
The idea of the mask is to mimmick training at altitude where the % O2 in the air is a bit lower.
Your body adapts to having less 02 when training and compensates.
BUT, unless your sport demands greater endurance at an elite level ( runner, boxer, wrestler, etc) wearing this mask would be silly.