Having the predecessor to the Aqua-Hot(Webasto), I have no where to add Aqua-hot fluid so I have to assume that engine coolant is in fact the same coolant being heated to flow to the registers? (that's a question). I finally had my system serviced in "Q" this year...being from So Calif, I never gave it much thought but it hasn't been working in a number of years, like 8 years. Make a long story short, the tech had my unit up and running in 5 seconds after sitting idle for that many years. The Nozzle was still functional, the fuel filter was working and it actually ran very efficiently(no smoke). Obviously, I had the tech service it(new filter, new nozzle and also I had him replace a marginal heat exchanger....so Im a happy camper now with good heat again. (the nozzle apparently was the original from 1996!!!).
I realize this older system doesn't really address the OP's question but in a way it does.....the basic system(mechanically) is the same. Of course the newer models have the electric elements and other upgrades...but as far as a well made product goes...I'd have to give it a thumbs UP!