In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Heat the DHW while not there?
a digital Intermatic timer on my MPI/Monitor DWH heater but set the temperature at 140 degrees for when it is on to kill any nasties. I encourage you to do that.
Tepid water is a dating bar for Legionella.
Viessmann Vitodens has a specific cycle to roast the little buggers and allows for setback so you are right, there is an application for this.