One of these came in one of the bathrooms in my house… a Kohler-Mira Sport Shower. It’s an electric shower, so it has one cold water line in and heats up the water in the little box.
It has the most fantastically terrible user experience - when you turn it off, it cools off the internal water heaters with cold water (according to my plumber). So every time you finish a hot shower, it blast you with cold water for a couple seconds. Seriously.
What kind of designer/engineer does this to people!