I thought about a Ranco, Johnson Controls, or Inkbird controller but each had complaints and didn't seem to be an improvement over a good heater with an electronic thermostat so I never bothered.
Don't think they are very good .I have a 300w in 2 of my 300 lt tank's and every winter I have to add another heater to the tank's to get the temp right .In my third 4ft tank I have a cheap inter pet heater that heats the water to the desired setting yet these expensive fluval heaters can'.t
no I am just going to replace them one at a time I need the guard as my rainbow shark likes graze on the heater guard where algae builds up.