Good question
2 captain operations are prevailant in corporate operations. The captain who is designated as the PIC, must be allowed to be the captain. Even more so the captain who is acting as the F/O should be mature and experienced enough and have the grace to "stand back" and let the captain do his job. Once that is established theoretically the operation should be as safe as a Capt and F/O operation.
However when you go back over accident and incident reports, one or two of the biggest screw ups has happened when two Capts have been flying together, or two training captains etc., etc.