It is repeatable job with codpiece. After giving it to Isla you click it in inventory than it disapears. Talk about codpiece again to Isla and go grab it again, talk with Vampires and go back to Isla.
Every time you do it thats 50 exp reward when giving codpiece to Isla. But probably not worth it if walk on feet and fight your way on map to Vampires... And also fighting just Vampires and winning will give you 10 exp. And for 10 gp you can return back from Outpost to first town...
Thats good for some exp-runs if got enough of gold. Make a run than save game. Reload and make another run, etc.