>>1705533
If I'm not mistaken they're just duplicate copies to increase their Engraving level. Unless you really like them and use them constantly it's not really necessary to go for them considering they're other Heroes you can use plus they're somewhat expensive. But for reference when a Hero's Engraving Level is increased they get extra stats. 6 HP, 3 Attack and a 0.2% View Power reduction for every level. So at level 100 the Hero will get an extra 600 HP, 300 Attack, and the View Power needed for their Skills will be reduced by 20% of the required value.