This reminds me of the woodwork workshop back at school, where you would start filing the edges roughly and then smooth it slowly my using softer sand paper :-P
It works amazing! First I use it to shape my nails then to smooth them step by step. And unlike other flies which leave your nails white of the edges, this gives a really nice look and feel. I use it at least every week and I always have it handy in my bag just in-case my nail breaks during the day.
This great tool does it all. One of the great features is it tells you on each side exactly what it is for, too easy. I love the fact that the emery side is not too harsh and it dosent leave your nails rough. My favourite part is the buffer. When I dont use nail polish I always buff and my nails are left super shiny and looking healthy. A good value all round nail tool.