Overall, best nuking piece after magic burst update.
Just a reminder, magic burst affect your magic dmg with 2 factors:
1. factor due to how many steps skillchain were done. Before update, it was a single multiplier of 1.3, increasing 5% each extra skilchain step. This was doubled, so your burst multiplier is 2.6, increasing 10% each extra step.
2. factor due to magic burst damage bonus, thats where this piece come to play. It caps at 53% considering traits, so your BLM will need extra 40% to cap, while SCH needs 44%, RDM, BLU, NIN 46%. AM II merits reduce the amount you need also.