I think it is also known that the signal is weak, since there are so many other unknown factors, and that makes it hard to discern from the noise (or perhaps ea

I think it is also known that the signal is weak, since there are so many other unknown factors, and that makes it hard to discern from the noise (or perhaps easy to cherry-pick results). So it is possibly still an open question of whether has an impact in the short/medium/long term, whether it requires better compliance levels, or whether it simply does no harm to wear them. It seems that the measurement problem is difficult without challenge trials, and it is unclear how that could be done blinded nor even ethically.