What is Reddit's opinion of Laing LHB08100093 AutoCirc Recirculation Pump with Timer and Adjustable Thermostat?

From 3.5 billion Reddit comments

Do NOT install a recirculating pump on a tankless water heater unless it has an aquastat and it is rated for it. The reason why is the tankless turns on when there is a demand (flowing water above 0.5gpm for almost every modern model). If the hot water is recirculated to the cold water inlet, it will eventually have water temperature equal to what the outlet temp should be. The unit will fire because it has a demand, that already hot water will get excessively hot quick, the unit will detect too hot of water and will mix cold (it has a thermomixing valve internally) to try to temper the water, which it won't be able to. The unit will shut itself off as a safety precaution because it thinks something is wrong and you will have to turn it back on manually or shut it off and turn it back on constantly. Eventually the thermomixing valve solenoid will fail and it will stop operating.

More advanced brands, like Navien, will have an aquastat power plug on the PCB and dip switches to change when a pump is being used. The Navien NPE-A models have a recirculating pump internally already.

Bell and Gossett and other brands have thermostatic recirculating pumps that you install under the sink, but it requires a 120v outlet and they run anywhere between $400-$550. That pump can be set to 95° (which I recommend) so it gets water moving so it is hot already and will reduce the wait time. However, a recirculating pump is only as good as the distance and volume it needs to move. If where it is installed is too far, it will not create the 0.5gpm the tankless water heater requires to turn on and you just wasted $500.

If you would like more information, please let me know. I don't want you to ruin a very expensive piece of equipment. There are A LOT of plumbers out there that don't know their asshole from their elbow and think a water heater is a water heater.

Edit: Example of the pump I described below.

https://www.amazon.com/LHB08100093-AutoCirc-Recirculation-Adjustable-Thermostat/dp/B0055NAOJ4