Not to argue that the 20mm cube won't work, it will, but the nice thing about the stacked cube is that will reveal bridging problems, inside dimensional issues, outside dimensional issues, solid layer problems, cooling issues, etc. I like it better than any other calibration object because it takes care of many things at once and shows you where to focus your efforts in firmware and/or slicing. The small, 5mm cube at the top will always reveal if you are cooling each layer properly. It really is a useful object that does it all at once.