Somebody ran some numbers, and calculated the break even point for an average home is to run the pump about 2.5 hours during a day. Use it less than that, and you save money, run it longer than that and you spend more (but does not take into account wasting water as part of an environmental event). So, running it on a thermostat, or a proximity sensor, demand switch, or limiting the run time, and you'll save money on both heating costs, electrical, water (remember, if you don't have a point of use or recirculation, you may waste 2-gallons or more each time you want hot water - even though you didn't actually get to use those two gallons, you paid to heat them), and sewer costs. Also, keep in mind, it costs energy to pump those wasted gallons to your house, then it adds to the sewer treatment costs, which uses energy to move it back to the treatment plant and actually treat it. So, to wash your hands with what may only take 1/2-gallon, if you wait for warm, you are using 2.5-gallons. Multiply that for everyone who washes their hands after using the bathroom, washing dishes, running the DW, taking a shower, and it really adds up to wasted water AND energy. Recirculation, done right is not only cheaper, but more convenient and saves significant amounts of water overall. Some locales are mandating it in new construction as part of the green initiative.
The unit I have is on a timer so it runs for a few hours in the morning, again in the evening, then most of the day during the weekends. It differs from most of them out there in that it has a user adjustable thermostat and only runs the pump when the temp drops below your set point. It probably runs maybe 60-seconds, every 10-20-minutes depending on the temp in the room. I have it set where the water is warm at the vanity, but it's essentially hot everywhere else in the house. Cycling will wear the pump and control out quicker, but so far, it's lasted 6-years, and still works as well as when installed.