I saw a similar one on the Wikipedia article for capos a long time back.
Not much use for a bass sadly: looks like you'd need six strings and a (thin) guitar neck to use this, unless there's a bass version
I use a simple Dunlop capo on my acoustic because it's strung with lighter strings. On my electric (heavier strings), the capo doesn't really clamp down all that well.
Edit: apparently this is not a new concept: see
http://en.wikipedia.org/wiki/Partial_capo (the url and text tag combo is not working @#$*%

)