Note that there is a bit of an issue with upgrading from Golden Mega Charge to Happiness is a Golden Gun.  The gains on the primary side (Golden Pistol) is so small (+2x +3) I would recommend NOT taking it.  You can fire off consistent 5 second charged 210s with Golden Mega Charge and the upgrade knocks 70 off of that!  Plus, doubling the charge time from 5-10 on Happiness is a Golden Gun can yield 180 or 220...Thus, it is simply not a good move in my opinion.  Which is strange, because I don't remember this being an issue in SSA or Giants.  Nonetheless, it is what it is and I'm glad to have picked up on it here in SWAP Force.