I have a Reef Keeper Elite, and for me it was just added insurance and convenience for the several thousand dollars that I have invested in my tank.
The only cons to a controller are cost and many people find it difficult to program them.
The Pros:
* The ability to setup alarms to shut off lights, pumps, calcium reactors, ect... automatically in case of a problem.
* The RKE has the ablility to send you a text message or email if there is a problem with your tank.
* All in one system to monitor PH, ORP, Temp, and Salinity and control pumps and heaters based on those values or a combination of.
* Gives you the ability to convinantly turn powerheads and pumps on and off during feeding or maintanence. I currently have mine setup for feeding so that it shuts all of the Powerheads, return pumps, and skimmer off for ten minutes so that I can feed spot feed my corals without the food blowing all over the tank or ending up in my sump and refugium. After the ten minutes is up the powerheads come on and stir up any food that has settled to the bottom. Five minutes later the return pump kicks on then 20 minutes later the skimmer comes back online.
* Can control an auto topoff system and with the use of a salinity probe makes it very safe and easy to use. No worries about dropping your salinity in your system due to a leak.
All in all it has been good investment for me, even with the numerous bugs that the RKE had when it was first introduced to the market plus their customer service has been great.