Gaining invisibility is going to inherently be strong for any character regardless of class, race, or playstyle. Invisibility is often an investment of concentration or a rare and/or expensive potion, getting it regularly by landing a killing blow naturally lends a huge advantage.
Therefore I don't think firmly committing Durge to one or two classes or playstyles is warranted, at least not yet. After all, as others have already pointed out, we only know ONE reward/perk from giving in to their urges.
Not really...because it only activates when you kill an enemy. Early game or against bottom tier enemies it will work for any class but later on and against tougher opponents it would be a waste to have that on anything but a damage dealer. But it goes even beyond that, you need it on a character that actually benefits from invisibility for more than running away...you really don't want your front line damage dealers to become invisible because then all enemies start focusing on your squishier party memebers. To make proper use of it that cloak has to go to a rogue...there's no other class for it really...high single target damage and hits a lot harder from stealth. The rogue is designed to strike and hide on repeat. At an actual D&D table nobody but the rogue should take that item because it would harm the overall effectiveness of the party.
