Here's my first heater. It's an El-Cheapo plastic one, but it lasted about 5
seasons. My current one is a metal cased heater, and more the "deluxe" model.
As far as how well they work though, both work great.
As you can see I have a fairly long duct on it, so EVEN if the heater burst into
flames (highly unlikely since it has a built-in thermal fuse) my plane is still safe.
With these heaters, I see initial oil temp reading (100F) within minutes
of engine start. Even with 0F outside air temp.
Jeff