They are a very good filtering option, as they are very versatile in what you can do to them, and add to them as well. They keep your tank from being cluttered, also. You can put your heater, protein skimmer, uv sterilizer, and most other hang-on or drop-in equipment all in the sump and all you would see in your tank would be the siphon and return tubes. The only tricky thing about them is keeping the level of the water in the sump at the proper height to allow for power outages, to keep from flooding your house. lol