I’d keep the denim one; this is an unusual enough item that I feel like a duplicate wouldn’t get used enough. I try to only buy dupes for core or classic items for that reason.
Just an update, I returned the metallic marine sharky coin case the last time I was at the outlet, and kept the dark denim shark case.
Of course I bought something else when I did the return because I can't seem to help myself! I got the Resin Hibiscus Bag Charm F29815 GD HOT for $21.60 (MSRP = $90); but at least I resisted buying the blue steel bandit bag that was 70% off!