I think it would be beneficial, really. It'd be like a normal humanoid creature being able to wield a two handed weapon with one hand. The larger weapon would only tie up one side of their body. And if an Eyphy trained with it, then they'd be used to it. I don't think they'd be able to do it with something like 5 points of skill in the weapon, but 15-20 and they'd be able to get pretty darn good at it, it would seem. They'd probably still have to take at least a few points in body building to have the strength with the arms on one side to be able to weild it correctly, too.
It was just a thought. I wasn't sure if it'd work or not. Thanks for hearing me out with it though.