Thats a strange one alright. I have found over the years that a combination of a battery blanket and a block heater will get your car through the coldest winter with no problems so it is very useful on a winter vehicle.  However as a rare accessory this is not the most in demand one I can think of these days as no one I know actually runs their vintage vehicle through the winters so it would likely stay on the shelf again.

This might be a fun item to show American visitors to see if they can figure out what it could possibly be, as many of them are baffled already by the cord sticking out of the hood for the block heater.

I suppose it might be cool (so to speak) to install it just to make the point of how tough your car could be.