While a 3D printed prototype might be acceptable for evaluating its shape, there is no way to test the material characteristics if your prototype is not the same material as the production part will be. Another issue cited in Kazmer’s study was surface finish.
While the surface finish of the part may vary according to how good (expensive) the 3D printer is, it is still no match for the smooth surfaces attainable with polished steel injection molds. Last, but certainly not least in the list of quality differences, is the issue of tolerances.