This is a variant of the Dunlop Elastic Capo, much-loved of folk guitarists.
An extended bar slides under the strings, and sits over the length of a fret, raise the action to a better height for bottleneck playing. An adapter raises the action still further, to near squareneck height, for lap-steel playing. This alters the physical length of the strings, so you WILL have to retune. You won’t be quickly changing keys between songs with this capo. In practice, it will convert your regular guitar into a slide guitar for the duration of the gig.
It works as a normal flat capo; BUT be aware that if used on a curved fingerboard, the first and sixth strings will buzz.
A useful accessory if you are doing any amount of slide playing, or want to experiment with lap-steel styles. Otherwise it’s a bit of a gimmick.