It would appear, for a human, as an oversized glove with three (sometimes four) stylized claw like protrusions and some odd wrist strap. The claws extend out beyond the hand just slightly. Wearing the glove makes doing much of anything with their hands difficult as the claws overhand and their are quite heavy.
Humans who specialize in unarmed combat have utilized these items in the past, but they are not created for humans. They are created for one of the Clawed Races to use.
If the being has claws, the Wvyrn’s claw will adapt to their size and shape. The metallic claw overlays the back of the the beings natural claws, enhancing them in terms of size, length, hardness, and some would say beauty (if one likes the Draconic/ reptilian motif).
There is not just one Wvryn’s claw, there are many of them. It was the "weapon" of choice of a paradraconic society from times past. Every now and again, one of the magical clawed races begin to make new ones.
There are non magical claws, but most are made by magic, thus having additional enchantments. The Claws grants a nominal increase in one’s ability to hit. It will also allow the creature to strike things that are spirit based (ectomorphic) and magical.
The claws increases the damage done by an unarmed/ claw attack to that of a Great Sword or Twice its base damage.
The Claws grants a great deal of defense, just for the claw area. This allows for attacks against targets of such hardness it would normally be impossible.