I'm not sure quite what's the point of a capo with a bit cut out of it. OK, if you only ever play that string open then you've got a differently-tuned string, but what if you need a different note on that string? Surely you're just back to the normal fingering then. I don't know about anyone else, but I don't have a "spare" string on my guitar that I can devote to solely being a drone string - they all seem to be in use for something at some point!

Grab.