Ditto.
I have this option and I still don't really notice any heat until things get warmed up (engine wise). I believe I read somewhere that it was supposed to increase the cold air temp by ~ 30 degrees. So, if it were 30 degrees outside when you start the truck, the supplemental electric heater should have you pumping out 60 degree air from your vents almost immediately. I have not experienced this.
Granted this is my first diesel, so maybe i'm getting a whole lot more heat quicker than the rest of you guys.
Just to confirm what has already been stated, this unit is not intended to heat up the engine block any quicker, it's just designed to provide warmer air to the cab prior to the engine warming up .