Seriously! When to upgrade anything is no less than 600. Not even able to purchase unstable cores is worse than a joke. It's a screw you and your time playing the game. If there was a way to purchase them like EVERY other resource in the game, them maybe my time playing towards level is worth being spent playing. Not even multiple characters is worth of being played, given vault space and MULTIPLE armour sets. Who thought it would be a great idea?! It's a joke