I have it and have heard it's not really worth levelling. I love the gun model and it feels fun to fire so I'm kind disappointed that it doesn't seem very viable.
Would it be broken as a secondary? If it were a secondary weapon I might see more people using it. It could be somewhere between a shotty and fusion rifle.
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I have it and am really disappointed. I think if they added an element damage it would make it more worth while.