I have the XB20. Charges on 120vac and 12vdc. So far so good. I bought it late in the summer. Used it once out on the trail last fall. Haven't been out since. Was very refreshing having a hot shower after a cool night in the RTT. It heats up well past comfortable (for me, the sweet spot is 113F) when you cycle the water twice through the unit. This is because the burners are only capable of a certain delta T. So if you start with 35 degree water, it will take a couple cycles to heat it up.
Only issue I've noticed so far is it "overheating" and shutting off on initial start up. This is because the pump is still priming when the burners fire, so the little amount of water inside the unit overheats and shuts the unit off. So you just have to reboot it, and away you go once the pump is primed.
Overall, pretty good quality and performance. I would definitely buy again.