As I said earlier, I've been very satisfied with the Reefkeeper controller for many years. But I also have to point out that as the years passed, I ended up using fewer and fewer of its capabilities. Originally I used it to control the heater, a chiller, the lights, the powerheads (wavemaker mode), and monitor pH, and to provide pump standby mode for feeding and water changes. Since originally installed, I've changed my lights from MH to LED with their own controllers. Because of that I also no longer need the chillers. My Maxspect Gyre has its own controller. I've always used a separate top-off system. My dosing pump system also has its own controls. As of today, the only thing I'm using the RK2 for is temperature control and pH monitoring. Everything else is done by separate controllers.
With the right peripherals, a more modern controller would allow me to hold tighter tolerances in the water by monitoring salinity and pH and automatic dosing, but the cost for this would be pretty ridiculous. At this point I could easily just pick up a separate heater controller system and a pH monitor to replace the RK2 and be right where I am today. I question though, whether there is really any separate heater controller that's as accurate as the RK. I have a brand new RKE system sitting in the closet, never used because the new system I bought it for never happened, and the RK2 is still doing everything I need it to do, which really isn't very much.
