I have a RO Classic 160INT on my 120g...2 years now...medium stocked tank and the performance is sub-par. I never can get good skimmate but that could be from a multitude of causes like not enough bio-load for the skimmer to pull crap out of the water. RO pros: quiet, easy of operation, ease of cleaning/maintenance, cost, fits in my sump and cabinet; Cons: overkill for my current tank needs? Design flaw of the skimmer? (this is a retired unit so it leads me to believe something might not be right with the design concept/equipment).
I may replace the RO in the next few months and if I do I'll replace it with a Skimz if that says anything. Both have a good reputation but one will win in the end and right now, I'm not sure it to be the RO in my experience.