is completely relative to the observer. a piece of shitty fabric over your face won't stop n95 levels of transmission but it is better than nothing. To some of us, it's "worth the time" to be less likely to spread even if by a very small margin.
Read the conclusion, what their study actually found: "We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility"