I grew up around an aircraft mechanic's hanger and recognized the cable type immediately. It's used as linkage on the controls of small airplanes and is strong, light and rustproof. Not mission critical for keychains but a nice lightweight alternative to heavy key rings. If you only have a couple house keys, keyring weight is no biggie. I drag around nearly two dozen keys so being able to organize keys on lighter and fewer key ring holders means a significant reduction in weight and bulk. I ditched my heavy key rings and never looked back. As long as you tighten well, they won't unscrew and are secure. If you're paranoid and don't plan to remove keys, a dab of Locitite Red will ensure it will never unscrew.
Besides keyring duty, I found they make great safety wires for camera bags and instrument case straps. I've had a strap hook accidentally open on a bag full of photo gear and the works fell on the floor. Thread one of these through the D-ring and strap end and you have a perfect safety wire, insuring your goodies won't hit the deck when the claw hook gets bumped.
The product I received appeared flawless and worked perfectly for its intended purpose. After 6 months of use I've had no problems with rust or failure. Great little gismo, ideal for both keychains and as a safety cable for straps, bags and other gear.