How would you control a heater? Calcium reactor co2 solenoid based on ph readings in the reactor? Speed controlled pumps? Kessil brightness, color temp? Will it email you if the temp is too high/low? Float switch in sump to trigger an alarm for overflow condition? Lights off when overheating? ATO?
All of these manufacturers make their own controllers. My finnex heaters are controlled by a finnex controller. My maxspect gyres are controlled by their gyre controller. My kessil lights are controlled by a spectral controller. My ecotech return pump is controlled by a reef link. My temp is monitored by a Seneye that can send push notifications. My topoff is a 7 gallon container above the sump. I have a wifi sensor that will send me a push notification if it senses water in the floor.
I have two heaters if my tank overheats I will get a push notification and I can look at the power draw and see which is malfunctioning and turn it off.
And now I can control my tank when I am away from home if an emergency arises.