The fact is that natural refrigerant systems work well if designed, assembled and operated properly. They were designed and assembled by the refrigeration industry a century ago. Once the general public started operating these machines, the industry quickly found that there were big risks and liabilities involved with average consumers operating and average techs maintaining them. The industry quickly turned to CFC refrigerant to eliminate these enormous risks and liabilities.
Fast forward to modern times, and the industry is giving them another try. This time, there are warnings, disclaimers, and regulations attached to everything.
The industry has put a cap on the amount of gas the units can contain, as well as special training for their service techs. None of the oem's endorse, condone, or much less recommend retrofitting any existing machinery with natural refrigerants.
Meanwhile, the petroleum industry has been actively working with tons and tons of natural refrigerant every day for over a century. You can quickly count a few titanic disasters related to the improper handling or processing of natural gases.