When I started both my accounts (and the 100+ rerolls I did) I kept getting two Iris's at level 10 (well one at level 10 and one the next time I logged in). When I asked this question it was suggested that I use both Iris's with my Alissa on my black account, but I got Marr on my two plat account for a third healer. Even with that being the case I have been considering leveling the second Iris as my 4th healer for Immortal Beast, and any other maps that may need four healers. I have yet to need two cheap healers.