The TCX interview day is really professional, but they go to great lengths to make sure that you're relaxed and that your personality shines through, and is exactly as Marty172 has described. The questions they ask in the 2-to-1 interview are typical of airline interviews, mostly asking for examples of various scenarios and to get to know a little more about you.
I've successfully got through the application process and have been told that it'll be by the end of February before they find out if they have the vacancies at my bases of choice, so it's very much fingers crossed, but it'd be an amazing opportunity. I was really impressed by the interview day.