Don't get too worked up over it, or even spend money you don't want to with ordering.
Ferrules are mainly cosmetic anyway. Rubber will give no support with that tiny bit into the adapter. Plastic won't give much either....if a shaft is going to break....it is going to break!
Like I said, epoxy is going to fill any void, so if it's for your own use, screw any ferrule. I don't worry about the small shit myself. Only if/when I would sell the club would I go back and make it look 'appropriate', for buyers.
