They do not feel like they should take up an exotic slot; and their jobs can easily be done by many other things in the game.
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I haven't gotten any of them yet tho i watched Esoterricks vid on them and his statement about needing kills(hits?) to charge, was stupid. I think the first step would just be switch the ability to either an ammo conversion so you could pump out a bunch if you got the ammo and thats what you want to use it for. or just a cool down.