Very nice post! I want to add that there is a certain direction that the heating element needs to point when it's installed. Like someone else was saying earlier... check the directions that come with the part, for the specific frost plug and orientation of the heating element. It may or may not be a big deal, but I've put in a bunch of these things, on a variety of engines and they all are specifically designed for each aplication. 
 They only need to be plugged in for 1-4 hours before starting...it all depends on the temperature. Also, in my opinion, engine heaters of any kind will not only make for easy cold starts and faster cab heat but allow for better lubrication during that critical first few seconds after start-up. 
My '04 4.0 with 237k on all original drivetrain seems to like it!