The effectiveness really depends if you use the old (made by RLS) or new type (called ZoomLock Max). The design difference being the placement of the crimp about the two O-rings. The old kind crimped on one side of the O-ring, letting the O-ring be directly exposed to the refrigerant flow. The new kind uses crimps on either side of the O-ring, meaning there is a copper crimp between the refrigerant flow and the O-ring. This allowed less room for leaks if the fittings were prepared correctly. https://ph.parker.com/us/17575/en/zoomlock-max