AS far as I can tell, it makes fishing easier.
I believe it's absolutely required for the last fish on the list. If not the +1 version, then the +2 version.
Basically, it's worthless until near the end of the game, and by that time the +2 fishing skill accessory should come up.
Unless there's a trophy for having all accessories, I'm not sure.
Right? There are also cloaks for distance traveled and your reputation with people at the village. The reputation one is probably best if you're going to use them, but I used a 1/2 SP use/+25(or was it 45?) STR and swapped out the second as needed.
One accessory that comes in major handy is fro ma sidequest near the end of the game that massively increases your damage against ancient species. Makes the midgame onward Interceptions a breeze to S rank, but you'll still need to get good for the endgame interceptions.
I wish I knew about these accessories, it would have saved me a lot of hassle....
The fishing, I ended up never using an accessory for all the fish and I somehow managed, although I swapped Adol to another character a couple of times since that seems to make a difference.
The damage against against species one I REALLY wish I knew about. As you say the last Interception and the last Enemy Base attack ones were a nightmare. Most of the time I've been using 1/2 SP + Double Flash Move time or having to use the weapon type modifiers since it's just been Adol on his own.
If there's not much changed from the JP trophy list, there is one of for having all the accessories.
And the option to show loading screen tips is funny. It says loading will take longer if you display them, but the game loads so fast, you can't read them anyway, lol.
If you do want to read them, they're saved in the Adol's Diary. Last tab shows you all your various stats and below that are all the loading screen messages.