The simple blankets just retain heat, there are ones with electric elements you plug in (like an electric blanket).
I'm not sure how easy the current diesel is to start, there doesn't seem to be much complaint from overseas where they've been used for years. Use the block heater below 30 degrees F to take a load off the starter motor, and to give you heat much earlier. Should be good down to -20F . Not the same motor, probably harder to get spinning, but my cummins never had an issue starting even without the block heater. The block heater saves wear and tear.... come to think of it, the truck also had two batteries