I have wing mirror protectors on my wing mirrors (2017 A-T coach built). IMO they provide a good service for scratches and very light dings but in a major blow they wouldn't do much (I speak from experience).
I have cheaper silver ones that I keep shiny so that they can be seen by other motorists in the home that they will give me more/enough room when driving. I popped some memory foam inside them before fitting to try and give them a little cushioning.
They start from very cheap on Ebay; through mid range Milenco's at around 75 quid; up to the very expensive ones by Mirrorguard at a whopping 140 quid. These are for coach builts. I'm not sure how that compares for A/B classes though.