One of the questions is "why do you want one?" On a reef tank, many people don't have them at all, which would be the cheapest and easiest Not to be a smart one...but it does help to know why specifically you want one (LFS saying to, experience, fish only tank?)
There really isn't that much they can do that you cannot correct by other means i.e. (quantine, nutrient reduction for less algae growth). One thing it will do for sure is kill beneficial organisms. I have never used so im just being rude, many people use them and just luv um
Not to be a smart one...but it does help to know why specifically you want one (LFS saying to, experience, fish only tank?)