Ok, this has been discussed a little bit.. this particular thread has 234 replies and was viewed ALOT.....

http://www.peachparts.com/shopforum/showthread.php?threadid=63919&highlight=alternative+r12+freon

I hate to be cynical.. but your mechanic has an interest in selling a changeover... the people in the thread ( except for REDFOX selling Duracool ) did not...

Each day more of the R-12 cars are sent to that big yard in the sky... and therefor the DEMAND for R-12 may stay low for a good while...

If , here in Texas, your particular car does not satisfy you on the cooling... will your mechanic change it back free ?