Hi Robert
The crystals of the current terminals, have a protective film to repel dirt and fingerprints. This layer wears out over time, but with products like alcohol the process is accelerated. Alcohol damages this film by helping to dissolve it.
I do not advise to abuse this liquid to clean terminal screens with an olephobic layer. Once or twice they will not damage the screen appreciably, but to abuse continuously cleaning with alcohol if it ends up damaging it with time. With a cleaning cloth glasses should be more than enough to clean the screen, thanks to this layer commented (oleophobic)
Regarding the liquid protectors .... I would not advise much its use. I do not think it really protects anything and most are basically composed of alcohol, but this is my opinion.