It's mostly useful for tier 2-4 fishing spots, especially tier 4. It is as to fish there it's quite money consuming (to buy shrimps and then actually catch something useful). It all originates from the idea that only raw fish (the ones you right clicked) can be cooked/grilled. With tier 4 fish such as yabby the chance to get raw fish, meaning the fish didn't disappear or give you a clam when you opened it, is rather low. Then sum up the low chance of catching e.g. a yabby (which is the 'best' fish you can get from tier 4) with the low chance of opening it and getting the fish raw which could be then cooked to get the exp bonus and you will quickly realise it makes sense to use a graphite rod skin with a cooked fish bonus.
That being said I would consider it an S tier bonus for tier 4 fishing spots, and A/A+ tier bonus for tier 2-3 fishing spots ( depends on your fishing strategy if you are aiming to get certain fishes such as Loaches [invisibility bonus] or the fish with INT bonus [can't remember the name of the fish and cba to open up the game] or you simply want any fish but also stand a chance to get clams when opening fish).
