That actually points out a pet peeve of mine: how so many people seem to credit Star Trek with firsts which are, in fact, old tried and true conventions.
I can't resist pointing out that Bette Davis made at least two "evil twin" movies: A Stolen Life
(1946) and Dead Ringers
(1964). And Boris Karloff did it at least once: The Black Room
But, yeah, the transporter twist was new.