I just visited some web galleries of bathroom remodelers in the US, and it looks uncommon to have external shower fixtures. They tend to bury as much of the fixture as possible in the wall. From the photos, I don’t get the impression they are using thermostatic mixing valves. But it’s hard to tell. Can anyone confirm or deny?
I think I might favor external fixtures because they tend to be much cheaper and also more easily servicable.
Even a couple of dollars more for a contractor is a lot when a thermostatic valve doesn’t add any value.
You can get inexpensive tankless water heaters.
You want to open the hot valve 100% until the hot water comes because it conserves water. You want to clear out the hot water line as fast as possible. Turning it to 70% just takes longer to heat up and you’re just dumping cold water out for no reason.
This is precisely what a thermostatic valve gives you. I don’t think you know how a thermostatic valve works. If the thermostat on the mixer bar is set at 38°C and you turn on the pressure control when the water in the hot line is cold, a thermostatic valve opens the hot 100% immediately and when the hot water arrives at the fixture it automatically adjusts. What you say about starting 70% open is exactly the problem you have when /not/ using a thermostatic valve, like the pressure balance valves that are common in the US.
(edit) also consider how tankless heaters have a minimum threshold for turning on. If you open the hot valve just a little, the heater will not be triggered. It must be open enough to trip the flow switch. It can be tricky to open the valve just enough to trigger the heat. A thermostatic mixer valve solves that.
I don’t think you saw the pic I posted of the cheap thermostatic mixer bar. Those can be installed by anyone because they are external. You just turn two union nuts until hand-tight then give ¾ turn extra with a wrench.