I wouldn't install a tempering valve unless forced too...then would uninstall it as soon as the inspector left. I've seen more than enough of systems limited to 120 F supply. Their delivered temps fall far short at appliances, sink, and shower. Somewhere between 125 and 130 F setpoint has been the sweet spot in various homes I've lived in. This includes tanks and tankless. The higher temp with 50 gal tank worked well to fill a whirlpool tub.
I've been resetting tankless to 130 F and that works well with "homerun" systems. I only set the jumpers back that limit them to 120 F when I'm handing them off to someone else. (I'm not taking responsibility for others being idiots.) The nice thing about having the ability to choose higher temps in a tankless is that for safety sake I can always drop back to lower set points, but I don't have to live with that crap.
I don't object to limiting bath/shower or some sinks to 120 F delivered...but that is a far cry from 120 F at the supply (outlet of the water heater) in most applications. And showers typically lose at least 5 F cooling from the showerhead spray, 10 F or more in aerated designs. Add in 5 F or more of piping losses, newer low flow showerheads, and "enjoy" a lukewarm shower.
Dishwashers wouldn't require nearly as much electrical heat if the runs were properly branched/sized and people knew how to make proper use of them. "Homerun" systems are a major step backward in this regard as they defeat preheating. Using several kWh to heat water is really inefficient unless your water heater is already electric (resistance.) I used the "sanitize" setting to booster to 150 F from 120+ in a prior home, but I always inventoried with truly hot water first--letting hand rinse during load pre-heat the water. I use air dry, because the water is already hot enough to sheet and drain and the dishes are hot enough to dry remaining film.