It's a powerful weapon to use in a safe situation, but you also must keep it safe until that moment. Adds difficulty temporarily and then it's an absolutely astonishing grenade. Throw it at a dragon with magic and watch it burn itself to death. Or be careful to not use any small magic (tough for puzzles and stuff) in order to have a super dangerous weapon.

Also you can just make up something that nullifies it that some enemy brings and it never works again after that, like the main enemy of the dungeon it was found in or so who had hoped to act as a trap to kill you with it (just like these characters probably did)