You can JS with whoever we have agreement with. Delta is a good one for Europe. You can't sit in the cockpit. Seat available only. Not sure if you can use the FA JS on those. Take a look at the JS agreement I think it is in the manuals. As far as friendly? I don't think anyone cares who we are. We are a dot on the windshield. I have never had problems once past the gate agent. That is the battle. Sometimes.