I have sworn that the next car we'll have will have (nice rhyming sound there incidentally) a Webasto.None at all The heated front & rear windows were on as well at that point as the windows were all completely opaque.
Yes, I know that it's extra Kg's carried around always, and it's not going to reflect on the re-sell price (never get the investment back).
But boy, what a relief it is to be able to "pre-heat" the car before you zoom off.
Very expensive pleasure, but what a difference it makes!
(Some people use garages, even heated ones, but that's even more expensive, so I'll go for the integrated option!)