A good investment
I use this product on my clients at work. Yes, it is a bit expensive, but if you look after it it will last you for years. Easy to clean and sterilise as well.
This file is perfect for very thick dry skin as it doesn't scratch at the skin like a normal 'cheese grater' style foot file does. It just buffs the skin off and you end up with very smooth feet. I usually follow with the #11 file for a perfect smooth finish.