I've heard several times the poverty level face masks, self or factory made make almost no difference.
Says who? Or, rather, does WHO say it?
If you don't have masks (or you have just 1.2% of what might be needed as we learned today) you would certainly say that they are not useful.
Anybody can see that all Chinese wear them ...and they seem to have new cases diminished (if you believe their numbers).
Independent variables or not?
I don't know.
As for the chinks, repeat after me: Communists Lie.
The virus itself is too small, correct.
But it has to be bound to aerosols or droplets to be inhaled and that is where the mask actually works.
The handling of that mask is critical. You have to put it on/off using gloves, discard them with the mask immideately, wash your hands, wash your face.
Alternatively, treat the mask with UV-C light or ozone, this also takes the stink and it can even be re-used.
The mask is an additional security measure, not a remedy. It just lowers the risk to get infected, IF you take all the other measures to protect yourself serious, too.