I agree with the Captain. UV-sterilizers aren't a sure thing at all for parasites since in order to kill parasites..or anything else, for that matter, like algae, it has to pass through the sterilizer and in a reef, there are so many places for the parasites to be sheltered before they attach to a fish, that lots are not "zapped" by the sterilizer before they can do their damage. And, you must match the pump that operates the UV-sterilizer very carefully so that the water doesn't pass through the sterilzer too fast for the exposure to the bulb to kill the unwanted organism.
Still, I have one on my FOWLR for an extra amount of "security" since I don't quarantine and it does offer limited prevention. This means, I guess, that IMO, the investment is worth it but there are no guarantees. To this, I'll add only that since I put the sterilizer on my FOWLR, I haven't had any ich problems which I had before.