As a clawhemmer banjo player (right hander) I can vouch that all the serious difficult work is done with the left hand on the fingerboard. All the right hand needs to do is keep in time and find a fingernail that can hit the right string more often than not. Even if it hits a different string, it will play something that fits in with the rest of the tune.
Of course, a mandoline is not a banjo.
Quack!
GtD.