The Screw shackle for the main isn't going to release unless you dont screw it in and get it finger tight. There a lot of ocean racers and offshore sailors that use the screw shackle on their mains. I've never seen a mid- to large sailboat with anything but a screw shackle.

I know no one that siezes the shackles. They might tighten them down more agressively on occasion, but that's it. Usually after a few days offshore, I find that the shackle tend to tighten itself more than ever loosening itself.

I beleive that the trigger-quick release is okay for a spinnaker or jib halyard -- but I wouldn't use one on a main sail halyard. I have those on my boat - spinnaker, jib, checkstays, and preventer lines where I need to remove them quickly.

I haven't seen a captive pin on a boat over 30 or 32' except a day sailer?

The trigger - quick release is okay for a spinnaker or jib halyard -- but I wouldn't use on on a mast. I have had them fail on boats for a variety of reasons. Further, they are a lot bulkier and would scar your mast.

I have never seen someone use those on a main, Larry. Do you?