It's about the same rng, I feel like? Bait = gig head, but you're not at risk of burning all your mp only to be told the fish sense something is amiss. You also don't waste attempts on maps unless you actively turn it on.

And the retainer does bring back spearfishing fish. It's just that like the regular fish, they can't bring you every last fish available, most of them you have to get on your own.