Started using the "shark bite" type fittings at work, prob 20 years ago. We never had a failure even with the earlier "quest" all plastic fittings. In general, they work like compression fittings, but the spring washer and "O" ring don't loosen with time and are effective on combinations of copper, plastic, even "funny pipe" That said, I too have some uncertainty re: how long that black "rubber?" O ring can last/seal. ...but then, how long will the plastic pipes themselves last? :>)