What’s that called?
Thermostatic (shower) tap. They are pretty common where I live in Europe. They actively adjust the water mix to stabilize output temperature. Also great for when somebody flushes the toilet or turns on a tap elsewhere in the house while you’re showering.
seems like a smarter solution than what one house I lived in did of just oversizing all the plumbing and having a recirculating hot water pump (probably could help prevent freezing, but it only got to -40 once or twice there) so you could run all faucets, the washer, and the dishwasher and still have pressure at the furthest shower.
You notice the difference in flow, to be sure, so oversized piping may still be a good idea. But the temperature shift will be soft and correct itself promptly.
