Yeah, a pretty terrible interval of time to conduct this study in Bangladesh. From Nov. 2020 to April 2021, only about the last third of that interval (mid-March to May 1st) might give you some good statistics. I understand choosing Bangladesh because of how relatively inexpensive it is to pay people there, but there aren't many large countries with lower per capita infections, to date, and most of Bangladesh's cases are more recent than the study's time frame. Of course, Bangladesh is also assuredly not testing as much per capita, so this all just sucks. To me, the study says "Hey, our error bars are small enough to be on the same order of magnitude as the measurement for only one deduction we were trying to make".
Muh physics says that a decent cloth mask should at least somewhat hinder the propagation of aerosols. I hated agreeing with Bill Nye (because he's notoriously a dick off camera), but it really is about as simple as holding out a candle in front of your masked face and trying to blow it out. Candle stays lit? Good. If you're emitting covid, it's got a better chance of falling closer to the floor instead of reaching someone else's face than if you were maskless. If covid is already in the air near your face, though, surely a cloth mask will do little, if anything, to filter it out.
Accusing pro-maskers of virtue signaling isn't completely without merit, but at this point, masking is pretty much also vaccine signaling in the US. Ironically, the people masking up are probably more likely to also be vaccinated.
... a big delta to work with
Careful ;). Not as bad as "Delta Air Lines", though.