On my Hobie 14 beach boat, I have used one of these detent pins to attach the lower downhaul block to the mast fitting for the past several years without issue. It works really well for quick install/removal. And it is lower profile as compared to a ball lock pin. Also with fewer moving parts to jam up with sand.
I have been a little reluctant to try it on our H16, only because we use that boat for racing and I like the extra security of a clevis pin. But based on my experience with the 14, I highly doubt there would be any issue. Once there is a slight amount of downhaul tension, the pin is locked in.
https://www.mcmaster.com/product/98404A006sm