If you want to get an argument ...Just bring up religion, politics or now (refrigerants)....Always Fun topics...

I think the legal side of it is that HC12 can be used in (Some States) as long as the vehicle has been retrofitted to 134 before switching to the HC12.....
Lots of debate on the flamability issues..... but from what I understand is that safety is not an issue as much as the EPA regs and the retrofit and the patent on 134A.....Its all about money in the end...
Europe & Canada uses the isobutane mix in millions of vehicles with no problems....and we know how safe those folks like to be.....I worry more about the 18 wheel tanker trucks going over 80 mph pulling a load of propane or worse.... than I do about a few ounces of refrigerant....not to mention the ~90 psi gasoline fuel injection systems on a lot of modern vehicles hauling 20 gallons of gas in the tank....Read and look up some of the DOT codes on the trailers that pass you going 80mph+ and you will soon put into perspective your highway safety concerns...

Before long any vehicle still using R12 will probably be required to have a DOT skull & Crossbones 24" square black and red sticker on each side of the car.....and can only be driven in daylight hours under 35 mph on restricted county roads...after you pay the $5000.00 annual Earth punishment fee.....If...the EPA GPS monitor is fully functional....with regular site check in....If your dreaded R12 was to ever leak....Federal law would force you to compost yourself as compensation to mother nature.....

But if it were mine ...I would stay with the R12....get it on ebay when you get your 309 cert for 20 bucks...just a lot less trouble after you find the leak........For now.....

__________________
1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)