In my opinion there is a lot of A/C Mechanics which don't know a whole lot about the job they do.
You must mean R134a not R143a.
Hydrocarbons such as Propane/Butane mix found in Hychill will leak out much slower than R12 and R134a, and the molecules are not smaller than the R12 or R134a molecules.
It uses the same gasses as LPG (Butane/Propane) if you want to look at it that way, but possibly more refined, different proportion of Propane/Butane compared to LPG for better cooling efficiency, also contains a UV Dye.
However many people have used LPG, or just Propane from their BBQ Cylinders in their cars without a problem.