I don't think any mask will fully acclimate a flatlander (like me) to the physical changes that happen at altitudes above 10,000. I do lots of cardio, hike with a pack, and get into elk country a week before the hunt. After a couple of days my body starts becoming more efficient with oxygen, and by the end of the first week things start to feel almost normal.
The central part of my training is to spend an hour or two each day on a stationary bike, and do some sprints up a steep 100 yard incline. Long distance running hurts my knees too much to be of any value.