Before purchasing an alternative refrigerant, consider the information at this WEB site:

http://www.epa.gov/ozone/snap/refrigerants/buying.html

There have been numerous posts here that these alternative products contain propane/butane or some derivative. Unfortunaltely, in many cases, this is not true. There are WEB sites available that list their content. Some do contain the aforementioned flammables; most do not.

A good number contain a large percentage of R-134A + some topping off of R-142B(one example).

They are not all illegal, but do require special handling and fittings.

If you want to learn more about this sort of thing, go to the trouble of obtaining a 609 certification and studying info at the EPA WEB site.

In the end, R-134A is as cheap as it gets and you do not need certification in most parts of the U. S. for this product.