Both cats will work. The "50" state cat is CARB certified and will have a little stamp on it that says so. Basically, the manufacturer paid a lot of money for the CARB to test and approve it's quality and HC/CO/NOx reduction capability.
The only reason the uncertified one would cause a problem is if a knucklehead at the IM240 testing station looks for a CARB stamp and decides to fail you as a result.
I refuse to live in an area that requires this nonsense so I am not keen on the level of enforcement/corruption.