We have one in our rig. It has the manual knob. Per the instructions, I adjust the knob based on the temperature of the incoming water and forget it. When I shower, I use the hot water knob only and throttle that to get the right temperature. I like it that way.
There are some issues with it. The first is that if you shut the water off while showering, you will need to aim it away from yourself when you start it back up because you will get a blast of cold water until the unit senses flow again. The second is that it's relatively low flow. But in a rig such as mine, that's a good thing for boondocking. Third, if I have to get up in the middle of the night and do anything that requires me to wash my hands, it really is a little too loud.
I've never had any issues with variable pressure from the pump. I've never had any issues getting it hot enough. I barely use any gas with it. I had only one issue where it cut off and I was able to reset that with the push of a button. Winterizing it is a breeze. No bypass required.
I'd own one again.