if you're tank is running fine, i wouldnt mess around with one. but if you're looking to lower nitrates and phosphates, i would def build one. i thought it would be hard to make one too, but they're actually pretty simple.
all they are is a seperate container where beneficial algae and pods can grow undisturbed......it can be an extra tank you have lying around to an empty trash can. you can have water from the main tank flow into the refugium then into the sump and then back up to the tank. or another combo if you wish.