iPod nano, like all iPods that came before (except for iPod touch) is a "media player," not a handheld computer. iPod touch is a computing device, with a real OS and apps; iPod nano is not. For most customers, "the whole point when buying a Nano," is NOT to use it for running. I use my 5th gen nano for running, but Apple did not design it just to be a run tracker. Like Apple Watch can be used as a health and fitness device, but Apple did not design it solely for that purpose.
However, I think my old nano does an excellent job, when used with the Nike+ sensor that goes on shoe (and the Nike web site to compile my data); the system is simple to use, reliable, and accurate. I've been using it for years. When Apple decides to drop iPod nano, I'm buying one before they are out of stock, so that I can keep using my current familiar run tracking system as long as possible (even after my 5th gen nano breaks).