Don't buy the stuff with ANY additives. You don't need any of the stuff. It is not likely to help anything, and it has the potential to really screw up your system.

But no matter what you add, be sure to purge the hose(s) of any AIR before you connect to the AC system. You don't want air in the system. Somehow, this vital bit of instruction seems to be left off of these junk kits.

And just to satisfy my pedantic side, Freon is R12. R134a is known by the trade-name Suva. I'd avoid Quest. Look for Du Pont.