I like the safety factor on the open turnbuckle of being able to see how much thread is sticking (holding) in it just by looking at it. With a closed turnbuckle I''m never sure if it''s just a quarter turn more and the shroud lets loose and the mast is over the side. My daughter''s Blue Jay has closed
turnbuckles, and they work loose frequently because the tape that holds the locknuts from loosening gets removed when the mast is pulled for trailering. Splash, and you''re out $16 for the new turnbuckle body. (She hasn''t lost the mast... yet - it''s always been the leeward shroud.)