I wouldn't want to judge a manufacturer on a single switch failure anyway, and we don't know if it was plaster. There was obviously dust in the air due to various decorating works and it didn't seem to affect any of the switched sockets or other switches that are in the same room; however, if I did carry out an autopsy, the result wasn't conclusive.
All I am saying is that, statistically, MK Logic Plus hasn't been the most reliable lightswitch in this house because there were 5 installed 15 years ago (if we count a 2G switch as two) and one failed. You could also say that the very old Ashley lightswitches haven't been reliable because there were 4 in use 15 years ago and one has since failed. The sample size is insufficient and there a lot of lightswitches in this house and some get used more than others. I just thought I'd add my sample to the other 5 pages as, combined, the sample size becomes more meaningful.