It works, but....
I had high expectations for this mask and bought it for running purposes.  I used it twice for running and the previous reviews regarding it collapsing making it difficult to breathe was correct.  After a mile or so, as you perspire and blow more hot air into the mask, it gets sweaty inside and pretty much feels like you're suffocating as you run.  I wish there was something that would prevent the material from collapsing into your mouth/nose.  I now use it when cleaning (dusty areas) and gardening (cutting grass) and it has held up very well after 4-5 washings.  It's definitely effective in filtering the air for allergens but don't use it for sports.
Rating: 3 stars