Well they've just added pay as you go functions but only, I think, in Brighton and Crawley. I haven't tried that yet though. However, for me, being able to pick up a ticket by just swiping the card at the gate or ticket validator is really handy.
Convenience. Ticket machines are often busy early doors at smaller stations, London Road can be a nightmare in my experience. You don't need to use the machine to pick up your ticket with the Key, you just swipe it in the validator.
They have. It's only available in Brighton (and Crawley) I think right now, but you can set up what's called keyGo, which you can use on buses and trains. On the trains it gives you the cheapest fair for the day, on the bus you have to get a day ticket at the mo.
Don't work for Southern but do have one. You do actually need to touch out/touch in as far as I understand it. The guards machines get cross when they check your ticket if you haven't touched in for a start, because it's not validated the ticket. Of course someone from Southern might tell me I'm...