At this point of the game it's very hard to move forward if you don't have enough boosters... That's annoying because it's a tricky circle: you can't move on, so if one of the steps to get golden bars is to pass a certain number of new levels you get stuck in the mechanism. And you play the same level for days missing the point of having fun. Developers should think about a less frustrating system of rewards. On the contrary the boosters gained more easily are always the same and they're always the least useful for stepping out to the next level.
