"In the shower, regulating the temperature is an issue. Turn
on the hot water, fine. Turn on the cold to balance the
temperature, and the slightest turn of the cold-water valve
gives us flat-out cold water; can't feel the hot at all."
I have never, not once, EVER - found a "one-knob" shower
control that worked in a user-friendly manner.
It's either scalding, cold, or next-to-impossible to
regulate the water temperature evenly with such devices.
In my opinion, the ONLY way to get shower (or sink) controls
that easily, accurately, and intuitively regulate mixed
water temperatures evenly and predictably is to use the
old-fashioned "two-handle" solution with a "hot" faucet and
a "cold" one, and then blend as needed.