From what I've been reading, it seems like the main complaint is that the Slim Line comes with a preset lighting timer that runs the lights from 6AM until 9PM, and you can't do anything about it. It seems like you can adjust which leds come on during that time span, but no matter what, the lights have to be on 15hrs. I also believe that if the power goes out, it screws the timer up and you have to reset it which sucks. I don't know if they fixed any of this with the new Slim Line-S or not...