I have not personally bought a refurbished 6th Gen iPod Nano but I have friends that have. When refurbished by Apple the iPod looks brand new. If the shell of the ipod was scratched by the previous user, Apple will replace the shell with a brand new one. So you can be sure it will have no scratches on the outer case. Yes the iPod is overall in very good condition. If your on a budget and dont want to pay extra, a refurbished Apple product is not a bad idea.
No one could possibly tell that it was refurbished unless I told them. Good way to save a few bucks. I also bought an apple tv 2 refurbished also. No issues with either one. If anything they are tested more rigorously to make sure whatever issues they had to begin don't arise again.