Thorn isn't worthless but I see no reason in using it over my The Devil you know. It has a much longer reload time and only a 6 round magazine compared to the devil at 12 rounds with a faster reload and mine has the mod for precision kills having a chance to refund ammo to the magazine so I've pulled off around 16 rounds before I need to reload it. Sure the thorn has a poison that does some damage per tick but when you take into account that you can fire twice as many rounds, and since Thorn has such a lower impact, each round is going to being doing more damage that dot doesn't make up for all that lost damage at all. The only way Thorn is any good is in pvp, in pve you're just doing yourself a disservice by using it when there are several other legendary hand cannons that bring plenty to the table, while at the same time freeing up an exotic weapon slot for something of more use. Like Icebreaker, or Truth.