I had one in my previous camper, a Lance. It was nice for having an unlimited amount of hot water. That was the only pro.
It took a lot of water and adjustment to get the temperature right, so you would waste a lot of water. If you tried to interrupt or trickle the flow, like to save water while soaping up in the shower, when you turned it back on, it was scalding hot, so you had to step away and wait for the temperature to get right.
If you have children, it would be dangerous.
It would be nice for a permanent or seasonal unit that didn't have to worry much about water consumption, not so much for us with a smallish water and waste tank.
It was quite noisy as well.
If you dry camp, it's not practical at all. I would not have another one. The two of us do quite well on our 6 gallon gas/electric water heater.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4