"Don't have the joint sealing capacity of compression fittings" ????? why then is it that flare fittings are used extensively in refrigeration systems and compression fittings are not? Refrigerants are notorious for finding places to leak from.
I don't believe compression fittings are legal in hvac. Certainly not in gas piping. Flare on the other hand is legal in gas piping. Compression connections are notorious for leaking, therefore illegal in gas piping.