Cheap and effective We use this in a working truck that was smelling of dried mud and horses. The change is dramatic with the truck's interior now smelling what I call "aggressively neutral" - hard to describe, it doesn't really smell *of* anything but it doesn't smell of nothing either. I don't think I'd use a unit like this unless there was a problem with smells in a car but the result is certainly preferable to stale eau de equine any day.
The unit is a little long and could get in the way if your outlet (aka cigarette lighter) is poorly positioned (too near the gear shift, for example).
wife loves it My wife absolutely loves this thing - she is pretty much always complaining it's cold in the house, but with this she's happy. Which, of course, means everyone else in the house is happy, too!
Not really necessary Maybe it is unfair to give this 3 stars... it does the job it is meant for.
But you don't really need it, you can easily froth milk in a mug.