They work
I first bought these about 15-20 years ago at a local shop (maybe the hardware store, maybe Walgreens or something like that) since I had new, expensive, heavy duty locks put in and found the head of the keys always dug into my fingers when I unlocked the door.  I ran out of them so bought these which work just fine.  I do always put a dab of Crazy Glue or hot glue on the stump on the inside that goes through the key's hole/slot (where you'd thread a chain or loop) before pressing both sides together over the key so the key doesn't slip around inside the cover.  I always have to kind of work the key a little inside the cover to get it to sit correctly.  These covers give the key a little more torque and cushions the metal edges.  When I run out if I'm still in need, I'll buy more (hope they still sell them).
Rating: 5 stars