I've been using these for years
They last and last, and the filing surface is just fine enough that it does a very good job, NOT (for example) tearing away more nail that I want to get rid of, or leaving the nail-tip rough.  (There's a rough side for quick "filing down" and a less rough side for the final smoothing.). ALSO, unlike emery boards, they don't deteriorate into useless pieces of cardboard.
Rating: 5 stars