Thank you for playing our game! Yes, the upgrade system was not easy to balance actually. I was testing a lot that it’s getting a) noticed by the player b) don’t scale like hell and breaking the game.
But I also wanted to have nice top-speed and oxygen at max level so people can enjoy that. Glad you liked it.
Also the red areas were hard to balance between keeping it playable and being this “challenging experience”. I already got also feedback that the red areas where too hard to see. Prob. some setting would have been helpful here. But glad to see it turned out well for you! Being more challenging was my intention there.