You do not need to play the entire game. Just watch the instruction video, and you will see that the mission system asks players to open a chest. However, this cannot be completed when playing as a guest.
I am not sure how a high-quality mod can be created if the modder has not properly tested the game or understood how limited the ruby currency becomes. I would not say rubies are completely useless, but after playing for about 15 minutes, you will likely understand my point.
If you are not comfortable testing the game, please feel free to ignore my feedback.