The STL file is ready for printing on a plastic extruder like a Makerbot. The bar across the middle is a hexagonal cylinder but it comes out nice and rounded when printed on a Makerbot. The model only has 18 faces so it can't get any simpler.

The openscad file gives you more options for how the barbell is modeled. You can make different versions, from the original BMW shape with hemispheres on the end to the abstracted version shown here. Some options will be more applicable to different processes. For example, maybe the rounded version would work well on a CNC lathe.