The mask is excellent. The boys don’t wear it much, only on extreme days (300+, 400+) but it fits as advertised. You would be amazed at how blackened the filter gets. We went through a spare set of filters in our first 5,6 months using it. Not cheap.
The only “problem” is almost like a social one: it’s like you’re implicitly criticizing your friends, or being inhospitable not having one to offer them because you’re the only one with it on. You stand out and it becomes a constant source of stares. Imagine someone’s taking you on an excursion, I wear one, they don’t? awkward. Or I entertain some kids in a park, my kids & I wear one, the children with me don’t? It becomes awkward. It’s sad how few people respond to pollution.
They are catching on here at Beijing Foreign Studies University, among a few international exchange students and some members of the European faculty.