Interesting.
I've heard from someone who did manage to crack his screen while defrosting it. He took it to Ford who replaced, but warned him that they wouldn't do it again as it isn't to be used for defrosting.
Though you do get tank drivers, who will only clear a tiny area in front of them before driving off, and leave the rest to defrost by itself.
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But not much use if the locks are frozen and the only can you have is inside the car.
Though, I don't bother with deicer, and just use WD40 on frozen locks.