I used to keep one on my keys back when I worked at a carrier store selling phones. Made life so much easier then.
In fact, the actual inserted part broke off years ago (and I haven't done phone sales in over a decade), but the main part of the body is actually still attached to my keyring. I haven't even thought about that until this post, actually.
The dude who sold me my latest smartphone this year had one long fingernail. I kinda thought it was a coke nail until he applied my screen protector and used the nail to separate the plastic backing from it. Aha!
I studied classical guitar in high school and since I could never keep my real fingernails intact I always had three plastic nails going on my right hand. That was a tough one to explain to the local bullies.