* If you think they're an effective measure for the public in general (which is probably closest to my position), then the variation in studies seems like it should still give you pause because it seems like the way mandates and messaging are implemented could undermine the usefulness. * If you think they're effective in individual cases when people do it diligently, it still seems like you should be worried about the possibility that a lot of people who think they're diligently and correctly masking aren't, including some medical professionals who are regularly exposed to the disease. * Honestly, even if you don't think they work at all, it still seems like learning why masks don't work would expand our knowledge of the disease.
Of course, we do know about plenty of factors that undermine mask effectiveness: people avoiding them altogether, people wearing ones that don't fit, people not covering their nose, etc. And of course researchers can skew the results with their methodological choices. But there seems to be enough variability in these studies that unknown or underappreciated factors could be significant.