They work really well, with the downside they are very explosive. However stories of airconditioners blowing up are really rare - it seems the risk is probably worth it for the environment.
Nearly all refrigerators/freezers in Europe are isobutane, and have been for 20 years.
https://www.youtube.com/watch?v=uJJvG10tUAw
They're pretty explosive when they have the right mix with air. This can easily happen in, say, a utility closet with a water heater or air handler, or a fridge in a kitchen, etc.
A small leak on the outside unit probably isn't going to be a big risk. A small leak on a unit in a closet with stuff that sometimes makes small sparks...