The D5, man that's a big heater. That's for large boats, trailers, stuff like that. That should keep ya warm and toasty.
I have the D4, which is not much different, tho.
The $1500 buck for a heater sounds like a stoopid amount to pay for a heater (I have the larger D4 at $2000), but it'll cost you at least that much to idle. It pays for itself the first year, and every year after that the money stays in your pocket instead of paying for the heater or the fuel to idle.
But the Espar Airtronics are air heaters, not an engine block heater, so no, the Airtronics won't heat your engine. The Espar Hydronic engine coolant heaters will. They are integrated in the cooling system of the engine, and the heat energy gained is then distributed through the vehicle's existing heat exchanger as forced hot air and this heats the interior of the vehicle via existing air vents. The engine is warmed up with the residual heat in the cooling water.