Equipping this weapon for battling the Unique Monsters such as Treasure Jar is recommended. With a very limited number of turns before they run away, every little bit helps. Also, almost every source of damage does the same one point of damage against them. Most characters will be doing far more than 10% per turn, making poison look weaker, but not against Rainbow Bird and friends. And it looks stronger in a Low Level, No Items Challenge, too, where 10% might be decent damage.
Shana will not get to use this weapon unless either she or the Virulent Arrow are hacked into the game.