on a straight gear vs gear comparison, given stat weights, Fuma is a wash at worst (and may even be a slight increase) with both Melee Cyclas and Allagan Curiass in any fight where you don't need to offload the lost Acc from using it in place of either (meaning, fights outside of Coil) other chest piece.

the Melee Cyclas is really good for substituting in better Allagan stuff in other slots and still being Acc capped for Coil, though. I wouldn't call the piece nonessential if you have a lot of Allagan Coil drops.