Yeah heard of the Rear screen shattering on the Meg II with some folks tho I'm sure many have used their rear screen heaters with no ill effect.. strange one what.
i really dont know mate,i dont use the rear heaters as it a well known fault with the megane rear windows to shatter when you turn them on so i tend not to use it,i havent known it to steam up even in the winter time,as i tend to de-ice the car with luck warm water
warning to others
if you do try this to de-ice the car with water,only use very luke warm water
hot water will instantly crack/smash windows
Thanks for the info Deejay