I'm not a doctor, but my $.02 is that it will not help. While the mask may reduce your airflow, the air you're breathing in still has the same concentration of oxygen. At altitude, the concentration of oxygen molecules are lower than at sea level. In addition, the air pressure is lower which will also affect you. I'm sure one of the resident doctors of the board can chime in and correct me if I'm wrong.
The mask will only reduce the intensity of your workout. I believe reading that it'll increase the strength of your diaphragm but don't expect to miraculously be able to go to altitude with no issues. The mask doesn't address the primary causes of AMS. A fit marathon runner could be sensitive and get AMS while someone less fit may be genetically fortunate to not encounter issues.
Steve House, who is one of the big names in American alpinism has reportedly even tried the expensive altitude tents and reported no benefits whatsoever. If it's too good to be true...
By the way, if you're dead set on getting one, save yourself some money and just get these. They do the same thing.http://www.amazon.com/Israeli-Civilian-M...1415&sr=1-1http://www.amazon.com/German-M-65-Military-Specs-Mask/dp/B00EHWJ954/ref=pd_bxgy_hi_img_y