Both Freeze 12 and FR12 appear on the list of EPA approved substitutes (note that approved means as far as environmental factors - not compressor longevity or chill factor.)
The FR12 is listed as R416A HCFC blend, (HydroChloroFluoroCarbon), Freeze 12 is 80% R134A, and HFC (no Chlorine), and 20% R142b, an HCFC.
Freeze 12 distributors list a number of claims. One site states that it is a 'drop in' replacement for r12 - a clear violation of EPA law which states there are NO drop ins, and that separate equipment, labels, evacuation pumps, and fittings are required by federal law for each refrigerant/blend, and that they can't be mixed during recharge/conversion.
More realistic commercial info is at this site:
which also notes that new compressors are not guaranteed for Freeze12, but are for r134a. Most of the conversion info you will need can be found at the EPA sites. Manufacturers/distributors claims should be treated like the claims of Cigarette companies regarding their products not causing cancer!
BTW, my 87 was legally coverted to r134a 2 years ago, and I can't tell any difference in how cold it gets, just a slight increase in time getting to the cold temp. It is still capable of making me colder than I want to be, even during a SoCal August heat wave. My temp wheel is at the same location as before the conversion.