Industrial 12A is completely compatible with 134a. IT Is not R12, don't confuse the two.
Also you are not mixing anything as long as you stick with pag oil. as you need to completely evacuate the system. The only thing left is the oil. I vacuumed mine for two hours and leak tested it. No I definitely would not put R12 in, but normally you can use R12a which is what Joe Kincaid who makes these unit uses. I evacuated my car again and tried 134a. It seems to be working well so far, played with the volume a couple times and 2 pounds 9 oz seems correct. Give or take a couple of oz.
My sugestion is to only use 134a because I believe the orfice in the txv freezes up.
Need to drive it more to confirm it is working well.
Barry
Just another comment, you do know the orifice diameter is designed to the medium (refrigerant) in the system, don't you? On another note, nothing like muddying up the A/C tech world like something called industrial 12a (small 'a' per the specs). If the vehicle A/C world is changing the medium used again, I shudder to think how many mistakes are (or might be) made in the field. Oh my, how would you be able to tell what some mechanic put in there? Dang people can't leave well enough alone. I seen a couple of posts on the net about this stuff (industrial 12a). Just more ways to make us have to take our vehicles to some 'stealership'.