Compared to other factions, they seem very lacking.
You can't get missions from them reliably(In 2 playthroughs i could only get 2 missions even at +20rep) , and when you manage to get one the payment is a joke. You have to pay toll even at max reputation, which makes it even less desirable to befriend them. And the best(and sometimes only) way you can increase said reputation is just paying an extra at the entrance.
The Pirate haven outpost doesn't have any faction-specific "ill-gotten" goods(Besides the vending machine at the entrance), merchants sell the same old items you can get anywhere else.
So far it seems like you get more value from bandits by wiping them out instead of relying on or raising reputation with them.