The Taco system might use about the same energy and less water than the
manual (run water until it gets hot) method. A cleverer system might pump
cold water back into the hot water pipe at the sink, after water usage has
stopped, until the cold water reaches the water heater output, leaving the
hot pipe filled with cold water between usage bursts, allowing house air
to heat cold water in the hot water pipe, vs allowing stagnant hot water
to lose heat in the hot water pipe...

Nick