My opinion is that the problem with starting in sub-zero temperatures is oil that circulates like molasses.

I'm not knocking block heaters but it seems that cold, thick oil is more likely the cause for slow turn-over and poor lubrication than cold coolant which still flows like water. I don't know for sure, but it doesn't seem like a block heater in the water jacket would do anything to warm the oil. It would certainly heat the cabin quicker though.

Fortunately in CT those sub-zero days don't happen very often. When they do, I just lay a droplight against the oil pan sump where the oil pump pick up is. I don't know how much it heats the oil, but it does seem to help some.

I've also never been crazy about heating elements that run off of wire that looks like it belongs on a lamp!

FWIW