On Boracay I do small rust repairs
as much "scale" off as possible by hand and then treating with either phosphoric or tanic acid.
The phosphoric sort of works.
If the phosphoric doesn't give me satisfaction I switch to tanic. It spreads it's evil purple stain everywhere, but given a few days and lots of "encouragement" it seems to get the rust to a manageable level.
It might not be better than a needle gun, but your hearing will stay with you a little longer. The purple fingers get better with time.
I'm currently trying a vinyl primer, but I'm not sure I'd recommend it to my worst enemy.