Along with the standard early variations that come up repeatedly in the 1910s, there are also numerous little foxtrot variants that turn up only once and were probably not generally popular. Despite the name, the "Castle Favorite", presumably a reference to the famous ballroom dancers and teachers Vernon and Irene Castle, does not turn up in any source I have that is actually by the Castles. Instead, it appears in Edna Stuart Lee's Thirty Fox Trot Steps (New York, 1916), a wonderful little source for unusual early foxtrot variations. I don't necessarily rule out a connection with the Castles, but given how creative Lee was with variation-names, I am not taking it as a given without some actual proof.
Lee calls this a "rather difficult step, requiring considerable practice and possibly not adapted to ordinary social dancing". That seems an exaggerated level of concern to me; it's not difficult to dance or to lead, and I see no reason not to include it in social dancing other than it being too uncommon to bother learning.
