I think that when you have to play BO1 games in tournaments you need mirror matches, or the game will always be unfair and favour the player who picks faction first. An example of this is how all the BO1 games during SNF quali tourneys went, the high majority of them ended with the players picking faction first being also the winners.
This is terribly wrong, and a terrible approach. BO1 has no place in competitive play, ever. Doesn't matter if you have mirrors or not, BO1 is absolutely, incredibly terrible for competition.