HI Tom, I think there is one photo of a guy holding a weird early banjo with what looks like one of these on it.
As far as capo use in the "classic" era-- nada. All of the instruction books teach playing in all keys without the aid of a capo. They are not even mentioned. The only mention have found is in the intro to Converse's Banjo Songs where he recommends using one for matching the voice. Over 200 books and only one mention!
James Buckley mentions them but he was shilling for Ashborne and they held a patent for one, so.. selling goods.
There is no evidence that they were even used by amateurs.
It came out weird-- Try this...