I would think anyone who might be considering purchase of the unit. No way would I be interested if I couldn't use it for hot water only or hot air only. Seems to me like trying to get hot water from it ads way too much complexity and possible failure problems.
I don't think I'd be using this to heat my water in the summer
and it's no more complex than using the EcoTemp unit I have. To me NOT using this to heat water is crazy to me as the system is self contained. I've often laid in bed listening to my Espar cranking away and trying to figure out a way to heat up water so to me this combo unit is a game chagner. If you're gonna use up fuel (kerosene in my case) why wouldn't take advantage of the heat exchanger to warm up some water?
Granted, I wouldn't use this as an "instant on" heating source for my water but I like the idea of getting up early in the morning, turning on the diesel heating unit. It can heat up the cabin while heating up the 20g of water in recirc mode. I don't expect bath temp water but I bet washing hands and face first thing in the morning won't sting as much if the temps overnight dipped near freezing. Mind you, I don't camp in winter but there have been occasions when night time temps got cold.
For my showers, I'd still use the ecotemp unit to heat up water but if the tank of water is already not freezing cold, it stands to reason that less propane will be used in the Ecotemp for the showers and what have you. Anyway, these are just my thinking but I like where my mind is at!