I am talking about this highly rated foot file here:
www.amazon.co.uk/gp/product/B01GJSIEJA/ref=oh_aui_search_detailpage?psc=1&tag=mumsnetforum-21&ie=UTF8
It does seem to work for a day or two after I have used it, but then hard skin reappears with what seems to me a vengeance.
Should I go back to a pumice stone? My areas of concern are mostly the sides of the big toes near the nail and the inner side of the ball of the foot. The cheese-grater seems to do a good enough job with the heals.