^ The next sentence of that article states:
Because of its flammability, it is illegal to replace R-12 with HC-12a in the United States.
I don't know specifically about HC-12a but you need to be careful about this. A refrigeration system is not designed to contain flammable materials, especially in a collision where vital components (such as the condenser) are the first be sacrificed. Also the gases are contained at high pressure which can make them more flammable or explosive.
I hear the argument that "gasoline is also flammable and there's a tank full of it already in the vehicle, therefore it's not a problem" - but this is not a good comparison. The fuel system was designed to carry flammable materials, the A/C system was not.
IMO, the performance of a R-134a conversion is 'good enough' and easy enough that you should just do R-134a. Despite some claims of the contrary, hoses and o-rings don't need to be replaced for R-134a. At a minimum you'll need an accumulator change, but you would want to do that anyway, even with HC-12a.
