I think the drawbacks other than cost of the unit are guesses at best. Yes copepods and other forms of microorganisms will die when they pass through, but no one has confirmed that it will deplete the population in the tank. If you don't like quarantining your fish then it helps keep outbreaks at bay although don't count on it curing a fish that is already sick. Also, it does keep the water pretty clear and helps prevent bacterial blooms.