I have a Webasto in my diesel 80 Series Land Cruiser, and it's amazing! Idling a diesel just doesn't generate enough heat for it to ever warm up, I could cold start it at -15 or colder, and let it idle for an hour and the needle would never budge from full cold. The webasto I can trigger from my command start remote, or use the timer, let it run for 45 min and when I go out to the truck and start it, the needle come about half way to operating temp, it blows heat, it doesn't run the glow plugs which means there's enough power for the windows to roll down and up properly in the cold, it's great. I can also continue to run the heater while starting my drive home until it gets up to full temp, as getting out of the downtown after work is just more idling.

That being said, they are way more than 2X the cost of a command start, more like 4-6X depending on what you pay for a command start.