Interesting topic. It made me do some reading. Some quick notes I caught from AC professionals at
http://www.autoacforum.com
"Freeze 12 is 80 percent R134a and when used with an R12 accumulator/drier the desiccant bag can break causing a compressor failure."<-- this is the comment that would make me run.
"Freeze 12 is 80% 134a and 20% 142b. It is EPA approved but does not have OEM approval. Using it requires a "Basic" retrofit including only evacuation, Fittings and Labels."
http://www.epa.gov/ozone/snap/refrig.../refblend.html backs this comment.
A few interesting threads on it:
http://www.autoacforum.com/messagevi...E=&STARTPAGE=2
http://www.autoacforum.com/messagevi...AR_MSGDBTABLE=
It is a replacement for R12, but it needs to be retrofitted, it should not be mixed. Plus if you mix it (or even just use it) you may have trouble getting proper AC service (if you are up front with the AC guy).
http://www.epa.gov/ozone/snap/refrig...tml#conditions
Many comments lead me to think you should try to find a can of R12. If need be the certification to get it is easy. Even I have the cert here somewhere.
http://www.macsw.org/certification.php
To use Freeze12 it would appear to be easier to retrofit to 134.