Do you mean an algae reactor, or are you talking about running rowaphos or something instead?
If you mean the algae ones, I made one using (I think) @Marty
's design and it worked well, until my phos and nitrate got so low the chaeto died!
Only minor issue is that coralline is a right git to clean off a curved surface!
Benefits are that it gains you space and the sump stays cleaner.
This is when I first set it up