game design is very bad, so easy to accidentally use crystal
progression is already too slow to get credits, it feel like log in to take 1 step forward, accidentally click without looking and waste 60 crystals on a reinforcement which you dont needed and take 200 steps back dont feel like logging in
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To be fair, once you reach the end of the campaign there'll be little to use crystals on except maybe multiplayer tickets (but even then it's not too worth it).