Grundfos says their "comfort system" uses "less energy than a 25 watt
light bulb," but it looks like that isn't the whole story. A foot of 3/4"
140 F pipe in 70 F air loses 30 Btu/h, about 10 watts, so when it is
running, their recirc pump might add about 1 kW to the power consumed
by a house with 100' of hot water pipe, or more, since Grundfos uses a
pump and a timer at the water heater and doesn't sense temperature at
the distant fixture. It looks like it pumps hot water continuously into
the cold water pipe at the fixture, thus making a lot of the cold water
piping hot and forcing a person wanting cold water to waste hot water
out of the cold water pipe until it turns hot again.

Taco seems to have a better solution. Their $300 006DM-PK plumbing kit
has a pump with a check valve under the sink, and temperature sensors.
I'd omit the preheat pushbutton and use it with a motion detector.

Nick