300 watts run for 2-3 hours a day is a dollar or two a month more on the electricity bill. I had a 400 watt coolant heater on my old LeSabre last winter that ran for far longer, and the additional cost barely showed up on the electricity bill. I'm talking maybe a dollar or two every month. It used little enough juice that I couldn't tell where it kicked in. It sure was nice to have working heat after 2-3 minutes instead of 10. The car also started like it was summertime. For my area, they're more a luxury than a necessity.
It goes on the bottom of the oil pan using adhesive. The directions say to put high-temperature RTV silicone sealant around the outside to keep road debris from dislodging it. For the plug, I'll run it out the top of the hood.
I'm far more concerned about the Cruze than the Fit, although both cars have potential issues. The Fit's battery is tiny, like 340 CCA tiny. It is running 0w-20, so cold flow isn't an issue. The only day it really struggled was the -15*F overnight we had, and even then it still caught. The Cruze has a proper size battery, but I'd love the turbo to get warmed-up oil faster. A full-synthetic 5w-30 should mitigate cold flow issues enough to not be of concern.
Really these are more luxury of having heat faster on a cold morning than needed for our cars to start. There's almost nothing nicer in the morning during the winter than to walk out to a car partway warmed up ready to spit heat. Besides, the wifey said she wanted a remote start, and we compromised on these.
