Seeing as the facepieces on these last for years, and you can get a few months of use out of a set of cartridges if you're only using them for stuff like taking transit or attending concerts/other large events, they're pretty inexpensive.
Oh, also, they're better than even N95 masks for keeping pathogens out.
I'm not suggesting wearing an elastomeric respirator 24/7, but in particularly crowded settings, they've got serious advantages.
as a bonus, you get to normalize looking cool as hell while being responsible in public