I think I have been subscribed for a month. Definitely since the beginning.
You continue earning Skullcrusher after the first month subscription. I have no idea if they will shuffle the dragon trust points available in the flight club chests, but right now you will always earn 5 of his points with a Hard chest. You also receive 90 runes, 40 eggs, 15000 fish, 15000 coins, either a 3 or 4 star sheep of any color, 20 energy points, a handful of random 1 and 2 star scales, and a basic draft token.
I don’t use the Medium or Small chests and can’t help with what the flight club adds to those.