Product review (5 stars): Works Great for its Intended Purpose
These are alot easier to use than the standard union with nut and ferrule.  Just push the tubing in until it bottoms.  And they don't leak as long as you cut your tubing square and clean.  They are meant for the 5/16" plastic chilled water tubing used on friges with chilled water dispensers.  Since that tubing circuit occurs AFTER the solenoid valve, it's a very low pressure circuit.  So don't try to use one of these on your 60+ PSI water supply or you might be disappointed.