The Key of the King's Law creates explosions, while not causing terrain damage they will destroy items, like mob drops you wanted from that powerfull enemy you used your new awesome toy on. Perhaps a line in the book that warns about this in a subtle way or a small change in the way it deals damage.

A second thought, it does create allot of those portals, which all make sound effects. It can be a pretty loud experience summoning 20 weapons. So as a suggestion, perhaps spawning 4-5 portals that summon 5-4 weapons each upon release.