Tried using a polarizer on 600D using live view and it was catastrophic: I couldn't see the polarization on the screen as I would using the optical viewfinder. Does this apply to mirrorless cameras as I expect?
It makes no sense, what you write. You do see on the screen what the filter filtered, also with a 600D.
Well this is what I saw, using live view polarization effect was barely visible while it is quite clear with optical viewfinder except for some reflections disappearing I could barely see any difference in live view mode
The screen shows the effect on the image.