My 98 Beaver came with the aquahot as a project - parts were in a box and the heating coil was leaking - an incompetent dealer service department let it freeze sitting on their lot. It took some work to repair the leak and put the whole thing back together, but I had no further trouble with it. I only ever used the diesel burner as my heat source so I can't speak to that, but I can tell you that if the burner is smoking you have fuel filter or adjustment issues. There are literally millions of oil furnaces spread over the Northeast and none of them smoke unless it's been years since they were serviced. Other than that read Ivylog's post for the straight goods.
I probably will install a heat pump and a heat-pump type instant tankless water heater in my next coach, so I won't need the Aquahot. I like the idea of heat pumps since they need a lot less service and are cheaper to run.