Once you've had it... it will be on your must have list. My AquaHot has a single 120V heating element that supplies all the hot water and heating when we snowbird is S Fla during the winter. Enough hot water for two back to back showers... the same at the end of the day traveling as the engine heats the water. Since I'm paying for the electric I use my heat pumps (most efficient way to heat) for most of the heating as it rarely gets below 36.
When boondocking you have to turn the diesel boiler on and the pumps, controller, and fans are all 12V. I do the yearly maintenance about every five years (300 hours) as I'm not using the diesel boiler very often. You can tell when the nozzle needs to be replaced as the exhaust starts to smoke and have a diesel smell to it. I also have a metal 90 degree sweep that I put on the exhaust if I have a neighbor on that side... partly to decrease the noise the burner makes.
The diesel boiler is around 40,000 BTU and the electric element is only 5,500 BTU. When boondocking I only turn the diesel on after supper for the dishes and for showers... 1-2 hours of boiler run time as it heats the water very quickly. I turn the boiler off after the first shower as there is enough heated water for the second one. My total cost on my A Hot is less than $250 in 11 years... some people pay that each year regardless of how many hours the boiler runs because somewhere it says you have to do a yearly maintenance.