Those mask won't help you acclimate to a changed environment. Being there at least two weeks in that environment will help you acclimate more. When those mask came out, so many of my Marine buddies used them, and before that, it was PT with gas mask. The only thing those mask do is make you know what its like to be exhausted and not breathe well. Like most hypoxic work outs, it will take a very long time, doing it most of the day, everyday, for months, or even years before you see any real measurable results. Not just a few times a week for an hour. As far as work outs are concerned, people are better off just running, rucking, lifting, eating right, and then giving yourself time to acclimate in a new environments. All the things people usually don't do.