It really depends on what you wish to control. The RKL is a fine, dependable controller, but it has its limits. You can only control 4 DA modules with it, so it is not very expandable. A typical setup for a RKL might be two PC4s, an SL1 or SL2 module, and some other module. There, you have reached your limit.
I would say it would prolly be OK for a simple setup, equipment wise, but if you plan on running/controlling multiple pumps, float switches, lights, pH probes, etc., I would look at the ReefKeeper Elite in DA equipment, or to the Neptune Systems controller.
Also, you say you get a pH probe with this. You will need an SL1 or SL2 module to use it with a ReefKeeper Lite.