Actually, higher classes don't seem to have a greater production speed, lower ones do. Try it on Zone 16 with the two on the far left. If you send everything to the bottom one, the top one grows faster. The effective is very small, though: 10 units to 9 or so.
Geez, is it just me or did the levels get crazy longer with the update? And where's the mid-level boss fights? I had one hall game with 5 princesses and no boss fights.
Instead of just the upgrade for cash registers, I'd rather purchase additional ones. I realize the wait time thing is a bug, but it'd add in some additional depth to be able to buy more registers instead of just upgrading to the max one. Also, what about buying back used records?
Great game! 4 stars is possible on 1939, but it's the toughest one IMO. You need to get one plane on each of your planes, then lead the first one to cross the second's field of fire.
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They do not auto-craft. They are needed to build advanced items.