Illegal or not, by one's country regulations... but surely razors or blades of any kind are dangerous, as said in previous posts.
I've seen home made butcherings done with blades... and never encourage anyone to buy those, although it can be bought in any drugstore and seem like a nice shortcut, and way out of paying for pedicures in salons and having them tell you it cannot all be removed/smoothed in one go... it's wrong and dangerous.
I'm trained and alowed to use disposable scalpels attached to scalpel holder and I'm holding that scalpel paralel to the skin and gently cutting, rather peeling thin thin amount of skin. If the skin is hard and thick. Otherwise foot files are just fine, among other products mentioned above.
But the main thing is - it's not just about removing the hard skin - you need to know how much to press that blade, how much you need to remove, and the main thing - you need to know when and where to stop. You never want to remove everything, because that's when hard skin will came back harder, or person will have painfull feet, or blisters, or infections... and that drugstore blades certanly do not let you be in control of the pressure and depth of the way you're going into the skin
... and yes, some people do have hard feet skin no matter what you do, but it's not because someone is a bad tech, but because it's just the way their body is... how the weight and weight pressure is balanced, and their spine condition, and how their feet lay down on the ground when they walk, and shoes they wear, and home aftercare... I hope this makes sense...
... my point is - it is sooooo dangerous in untrained hands. So if not trained and alowed, just don't bother with it, there are other great products to be used...
hth :hug: