I often have people ask if the Smart Recirculation Control will work with tankless water heaters. The answer is yes it will. The only comment is to look over your water heater's specifications and check if there is a limit on the temperature of the water going into the water heater. I have heard of one electric model that limits the temperature to no greater than the outflow temperature minus 20 deg F. In which case you can set the temperature differential in the Smart Recirculation Control to a large differential of 25 deg F and a small differential of 20 deg F.
The system should be installed exactly as if the water heater were a tank model. The flow meter goes on the cold water input to the water heater, the one temperature sensor goes at the outflow to the water heater and the other temperature sensor goes on the recirculation return line near the pump and before the the recirculation line T's back into the cold water feed.