Europin fan, my two cents.
Still cannot understand the advantages of Us system. They say that two pins are safer, pheraphs because if one ot two breaks, one can save you from loose the rig, but I have some doubts that one small pin can resist such a pressure. And therefore in us system the walls of the mast base and extension that receive the two pins seems thinner and subject to breackage. And it seems really unconvenient in many situations.
Never happened a problem to my europin extensions in more than 12 years, even in strong catapult caused by almost sudden stop in shallow water when I found a mud or sand bank. But I have to admit that unfortunately I'm not a waver (still a wannabe). And surely some chinastyle locking devices of some cheap europin extensions are to be avoided.
I await for answers from more expert surfers.