I also have a defa heater sitting in a box in the garage waiting for an opportunity to get it fitted next to the oil cooler - other things have got in the way this time round. The difference between the Webasto (meaningful heat in about the same time as our AUA car starts being able to clear the windows) and the auxiliary air heater (partially effective) over the commute journeys I use them for mostly is such that the AMF car is the one I use for winter commuting (or would be doing if I wasn't getting the gearbox replaced today) as it is lovely to have a jet of hot air onto the hands within 5 minutes of leaving home after scraping the windows.
Otherwise when I know I need clear windows for a quick start, I have 2 60W incandescent bulbs in clip-on mains holders that clip onto a cup holder at the front and the cubby hole behind the handbrake at the rear - overnight those keep a car either completely frost free, or else on a properly cold night, the frost remains soft-scoop consistency rather than welded to the glass. The garden extension cable from the garage goes neatly through the seals around the door frame to the driver's seat where the lights are plugged in.