OP is not an empirical study, but model-based one. The paper first assumes that facial mask prevents individuals from spreading covid-19, then tries to estimat

OP is not an empirical study, but model-based one. The paper first assumes that facial mask prevents individuals from spreading covid-19, then tries to estimate how it is effective at lowering the mass reproduction number. So this paper proves nothing about whether wearing mask is really meaningful or not in the first place. It is just assumed so.