they all seem to be made of substandard materials and aren't very robust or corrosion resistant. What I did on my dodger was to sew a batten pocket into the edge. This was filled with a small diameter carbon rod (like 1/16 or 1/8) which kept the ends stretched out and stiffened the edge enough that a few hold downs was all that was needed. You can use different diameter carbon for different situations. Also in the pocket is bungie stretched between the ends and tied off in grommets to allow replacement every 5 years or so. There are cutouts in the pocket to allow a loop of the bungie to be pulled out and down, to be hooked under a small hook. These can be had of a proper grade of SS, are much more robust and corrosion resistant than any snap or twist I have seen. A flap of cloth covers everything, so it looks like nothing is holding the cover on. This has worked very well for the dodger. On a removable cover you would have to roll the cover around the carbon rods (or remove them to fold).

I should have pictures of this but haven't found any so far.