Here’s what Kyser say about their quick change capos:
A Kyser® Quick-Change® is expertly engineered and built to last. It is reliable and does just what it is designed to do — clearly raise the pitch of the guitar so you can play in a different key without retuning or changing fingering. Seasoned professionals and beginning players alike appreciate how the Kyser® Quick-Change® helps them transpose their guitar in seconds, with only one hand. The beauty of the Kyser® Quick-Change® is in its simplicity. We pioneered this design and although often imitated, a Kyser® is never equaled. There is no substitute for a Kyser® Quick-Change®.