I have one in my master shower and it's fantastic. Of course, the water starts out cold (because the water in the hot water pipes are cold) but once it's up to temperature, it's very consistent, even if you have a toilet flush in your house which would reduce the pressure of cold.
No, this should be considered a failure condition for a constant temperature shower. I don't care how they do it, just bleed the cold water into a separate pipe off to the side or something.
We have sent people into space, I want actual uniform temperature water.
the way I do it is just turn the shower on about 30 seconds before I get in, which works the same with half the piping and less energy loss due to circulating hot water (but some water loss)
- not drop the pressure of the cold water at all
- drop both the hot and the cold equally (due to house input being limited)
The hot water is fed by the same input pressure as the cold, so they are the same pressure system. A temperature drop on a toilet flush is a pretty big fuckup by the plumber in the bathroom.