I have usually used the block heaters installed into the freeze plug holes, but I have a van with the heater-hose external installation as well. Both work just fine. As noted, block heaters are normal technology in Canada and the northern prairie states (and Alaska of course.) Not only does the vehicle start much better with a warm engine, but the lower friction means much-reduced fuel usage in the warmup period, apparently more than paying for the electricity. Also, reaching correct fuel mixture so much quicker reduces emissions and engine wear.

Not aware of people using the dipstick type around here, maybe they don't put out the same quantity of heat. Probably still help a lot though. Even a light bulb in the engine compartment makes a difference (as noted in prev post.) I've also seen heaters with magnets to hold them to the engine.