What do you mean by a "premium" preformed shower base/pan?

The 'premium', as they call it, is a better material with more choices in size and color. The pan is treated as any other pan/base with the tiled walls coming down over the edges. I'm having the walls tiled, just don't want tile on the floor.

The preformed bases are made with a slope and a drain location of the end, center or a grate-type drain along one end.

Here is an example.