It was an Espar. It was wonderful when it worked, but the glow plug needed to be serviced once in a while or it would soot up and stop working. You wouldn't know when until you needed it.
It's not simple to install those... with the ducting and exhaust and diesel supply and thermo controls and control computer; and I'm not sure I would use it enough to justify the expense (about 2-4 boat-bucks, depending). The Coleman Black Cat works well enough to take off the chill in Spring/Fall but I wouldn't go to sleep with it on. We can be comfortable in some pretty cool temps sleeping in fleece outfits under heavy blankets. It would be nice though.
The bus heater is relatively simple to install. Just fan power/control, and tap into the engine coolant at the water heater hose. All I'd need is two 1" holes in the engine bulkhead to the main cabin for the coolant/return, vs. a 3.5-4" hole for air ducting.