A UV sterilizer is kind of like a band-aid. It hides and doesn't truly address the real problem. Since it only works on free-floating organisms that are drawn in, it inevitably does not catch all pathogens. If you exercise proper quarantine procedures and set your tank up properly, you will not need a UV sterilizer. The real problem is lack of proper quarantine and husbandry procedures.
Example: In 12+ years I have never used a UV sterilizer nor had a Cryptocaryonosis break out. Why? I quarantine and exercise prophylactic countermeasures. YES, I have purchased fish that carried Cryotocaryon irritans (marine ich) however I treated it during quarantine and never imported it into my system.
One last concern is a UV sterilizer will kill or "sterilize" any phyto-/zooplankton you add to, or grow in your system. Something to think about...
What ever you decide is up to you, there are no bad choices, what ever works for you is best!