I just bought an 18 watt unit for my 180 gal. Whether or not its worth it, will be determined. Many lfs owners and enthusiast say its highly recommended. get and extra power head to pump it through the light and back to the tank. put the power head in the sump, like the big pump. beats tapping into the main return lines...
Yes, i think they are worth it. I look at it as protecting my investment.
Just put the PH in the main tank, use flexable tubing to get to the UV (on the back side of the tank)than a return line back to the main tank. You will have to use some elbows and stuff, but thats about it.