It clears misted up rear screen, heavy dew is another matter.
The Ampera is well sealed - check the door rubbers for example - the effect is to keep damp in the car, more so now coats are wet, worse if the air is on recirculate. For years I have used silica gel bags (2 off 1kg bags) to reduce the moisture. This works well and allows the demister to work.
Mine came from Aldi but there are plenty about - recharge by microwaving.
This type of thing, no Idea if this brand is good!
If the car is already wet then next time you are running the engine set the temp to max, cook the car and then open all windows to let the steam out!