I've found such a device once in a hostel in Germany. The device was from Amphiro. [0]
Being that hostels focus on savings, I understood why such a device could be useful. As for myself, after a day-long trip it ended up being a frustating shower. The thresholds were so low that you have to take a Navy shower to have a good grade. And the polar bear display reminded me that Germany is mostly coal-powered and that a KWh here has a much bigger impact on the environment than a KWh from France.
I got out of the shower cold, wet, and worst of all, not feeling clean. I wondered if it would not have been better not to take a shower at all. It sure would have saved more water and energy.