What is the difference between your Under Gravel Filter styles?

The Economy Under Gravel Filter has a flat plate, designed with more open space for better water circulation. Available in rectangular shape only.
The Original Under Gravel Filter has multiple plate construction for easy installation. It's advance design allows separate plate installation with optional flow thru set-up which can be used with a power head. Available in 3 shapes to fit rectangular, hexagonal, octagonal and flat-back aquariums.
The Premium Under Gravel Filter has a multi-level plate design. The larger plate sizes reduce the number of plates required. The added strength of the plates makes this filter most preferred by saltwater aquarist. Plates are strong enough to stand on! The molded gravel guards eliminate the possibility of gravel falling down the uplift tube. Available in rectangular and hexagonal shapes.

All 3 Under Gravel Filters include Lee's fish-saver elbow, telescoping ring for uplift tube height adjustment, Disposable carbon cartridges and discard-a-stones.