They say ~ Treat your nails to the ultimate nail file - a crystal design from OPI. This is made from hardened 100% non-porous glass with an ultra fine, abrasive 240 grit surface etched into it and will help to prevent your nails from chipping and peeling. It can be cleaned with ease and comes in a handy carry tube for storage and protection.
I say ~ Well as you know I don't like spending a lot of money on something so once again I used some of my tesco clubcard vouchers on BeautyExpert. I've used cheap glass files before and they completely failed, but these are totally different from those glass type files. This file is quite gritty and files your nails quickly, turning the excessive length in to dust.
I like the fact it you can file anyway over your nails you like without damaging them. Unlike emery boards you can wash it and that restores it to the original grit. The tube is a bit rubbish but you don't have to use it. Only drawbacks for me is the price and the sharp end as being so clumsy I often have jabbed myself with it.