I have a block heater on my tractor that is mounted in one of the freeze plug ports. For me, that's the way to go. All of my cars and trucks get those too.
I do have two of the Kats heaters I bought for my sawmill which has a 51 hp CAT diesel. The way the engine is mounted, it's hard to put the Kats on with full contact on the oil pan. I don't think heating the oil pan is as effective as heating the water jacket on the engine, so I bought a block heater for the sawmill, but I haven't installed it yet (thanks for the reminder - I hate working on engines in the winter).
I do use the heaters to heat the hydraulic fluid tank on the sawmill and I think they work very well for that.
- Marty