I would not trust them without a divider. I talked to a few other people after my trouble about them and I heard several of the same story. Get a pair, male kills female.
Maybe if the pair you are getting is well established and has a good bond you will be OK, but I wouldn't risk it. Often time switching tanks or shipping, etc, triggers more aggression when they are put back together. I would divide them to start with and only try them together when you are there to watch them. If the male is larger just cut a hole for the female. If they are the same size divide them to be on the shafe side.
Good luck!!