I had one on my '93 Cherokee, heater was not great and I had to park it outside so it helped a lot to be able to start the engine at 110°F as opposed to -15°F in Colorado winters.
If I was still living there and had to drive my D200 regularly I'd probably add one to that truck. Fortunately the coldest it gets around here is about 20°F at night. I would like to add one of the factory air cleaners with the heat riser since the exhaust crossover is blocked and it's not very happy the first 5-10 minutes of driving when it's cold out. They're pretty expensive these days though.
