I’d imagine at least some of the advice against buying masks is to prevent hoarding and a supply shortage where they are needed most: healthcare workers.
The masks can be counterproductive if used without discipline or training. It's not uncommon to see people adjusting their masks and scratching underneath them constantly. The masks are transformed into virus concentrators and rebreathers.
Are you aware of any studies on this specifically? Sounds very plausible but hard to weigh against the benefit of catching expelled droplets. I imagine the calculus changes depending on age, and whether your primary concern is preventing your own infection vs. transmission to others.
