This survival product is rarely mentioned. Most people won’t be able to test if it works until they need it, but at least it is cheap and easy to stash.
Scenario: you are doing your best to escape from a dangerous scenario, and do-good cops decide you aren’t being a good citizen. They handcuff you and head off to arrest more rebels. You pull your key out of your sleeve/socks/jacket zip, unlock the cuffs and flee.