<---- RK Lite owner. I have had nothing but good experiences with it. IMO the only reason to skip it is it can run a max of 4 modules... whether they be outlet strips, moonlight controller, NET module, whatever. Having a pH probe and/or using it for an ATO requires the SL1. Even if you used up all 3 remaining modules with PC4s, that will be a max of 12 controlled outlets. If you skip the pH monitoring, then you can do 16. You may be surprised how quickly you use them up once you discover how nice it is to assign functions to the controller.
When I do the in-wall build, I'm considering running the system with two RKLs. One would do just lighting, and the head unit will be in the viewing room (front side). The other will do everything else and will be in the back/equipment room side. This way I have up to 8 modules, and can control lighting when showing the tank to guests, and the other would be used from behind during maintenance, etc.