I don't need any of those 3 but i do agree that marble keys would be a much more useful and greatly appreciated prize.

I have so many marble stones that i reached the game limit and only get them from the event prizes.

S8 has added marble stones as a mining prize in addition to the coins and apples. Here it is definitely annoying when mining they only allow collecting 2 categories of bonuses so if i get coins, then ZERO stones because i reached limit and then finally find food...that last find comes up as ZERO bonus. How sad.