Well here in Blighty we would generally be confronting temperatures not too far below 0C, so hand-hot water is fine (I've been using it entirely without incident for half a century). Don't think I'd be using it if the mercury was thirty below. Point taken about more ice on the ground, maybe, though my car is parked on gravel, so that doesn't apply.

You could always get a windscreen cover, or improvise one with a sheet of cardboard or a newspaper. I've found that those de-icer sprays used on the outside tend to make the inside of the screen fog up, or even freeze up. I love those flowery or leafy ice patterns that can form, and I always take a photo or two.