Brand name is preference...
Skimmer injects air into the water in various different ways. While these tiny bubbles are suspended or moving through the tank water, they attract dissolved organics and other pollutants...as the air rises to the top, it collects and collects, it then enters a tube which leads to the collection cup. Once in the collection cup, the bubbles rupture and deposit what they had attracted in the collection cup for storage and subsequent disposal.
This offers many advantages...of these are, oxygenating the tank, and removing pollutants prior to them being dissolved and ending up Nitrate's.
Whether one needs one or not is a personal decision one has to make. They are not required, but most highly recommend them in the marine environment.
