Just reading general comments...
FLICK Mixer... would that work as a practical device..
Whilst it's not a bad idea, the problem I see with it is that it could easily be bumped changing the output temperature a great deal up or down on the desired temperature.
That's where a tempering valve comes in to its own, you need to make a deliberate decision to change the temperature.
Of course you need to get one that goes down as low as I want it to go. Thinking that the temperature I want is 30 degrees, I'm kinda thinking that setting it to 40 will allow the initial not-so-warm water to come through before temperature is reached, then the 40 degree water will blend and give me water in the machine at somewhere close to 30, achieving the intention of not having the washing machine heat any water itself.