I have had the S hook break on my Nacra 6.0 and then moved to the Quick release Shackle in your picture and really like it. I also had the S hook bend on my Nacra 5.5uni where the loads are much lower then the Nacra 6.0. S hooks are quick and simple but I no longer trust them. They will only let go when it is honking and then it is a clust F trying to jury rig the main blocks to a flailing mainsail.