Lol, in Germany those are only installed in shitty old houses with crap plumbing. They drive up the electricity bill like there’s no tomorrow. Just install adequate plumbing when building a new house and never deal with this problem.

That’s a thermostat and won’t do you any good if the plumbing is set up in such a way, that all outlets are connected in series. You need a parallel approach (manifold with large diameter branching off to all outlets).

You can also fill up the dishwasher over the course of a couple of days. Makes things even more convenient.

For the shower you’ll want the 18 kW, otherwise you’d have to shower with a tiny stream of water. What you have is meant for washing your hands (tiny one under the sink).