Having had it on one of my cars if I could have it without the expense I would have it straight away. In the winter months it is THE best thing if you store you car outside.
While your making your cup of tea in the morning fire up the car and 5 minutes later you get in, the seats are warm, the windows demisted and a much nice driving experience.
That said the one thing I would really really want on a car is total window closure - much more useful but a fraction of the cost...on most cars but not the Z