They're made from extruded plastic, like most hang on filters, so expect spider cracks throughout the plastic after a couple of years. The skimmer must be modified in order to be efficient. You'll need to run an air tube with a diffuser powered by a separate air pump into the skimmer chamber to get max efficiency.
If you plan on running saltwater, I'd suggest a much larger tank than a 30, unless you want to keep a pair of clowns OR 3-4 chromis and nothing else. Larger tanks are also more stable.