[Barnsnake]

I've never seen one of those, so I can't speak from experience, but here's my take on the pros and cons:

Positive:
I expect the installation is pretty simple.
It will make heat before the engine warms up.
It will make heat without the engine running (while discharging the battery).

Negative:
That's a WHOPPING load on the alternator and wiring.
The alternator load is parasitic on performance while a hot-water system is neutral or a benefit.
There is an immense source of heat two feet in front of the dash that we spend power and money to get rid of. Why not use it if you want cockpit heat?