It's useful for a single specific fish. I've found it...semi...useful trying to get the pearl shells for the relic. That has two fish in !! and pearl is on ! so hitting that and then ignoring the other !! until I get the pearl's ! is useful. Though even then it can take the ! forever to come up.

I definitely wouldn't want it useful only under Patience or Patience II. I've gotten better results for the relic not even using those because I went entire runs without a single ! coming up.

I do think 200 for one catch is steep and they should low the GP on that to make it more useful, especially if you're utilizing Identical when you need more than one of what you want. Or keep it at 200 but make the fish bug off for more than one catch.