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Are you referring to these photos from the rigging section? If you are, IMHO while plates like these may have applications for trout and smaller species while using a rod holder, unless the bungee was super tight, there may be too much play in it to really hold these down when alot of torque is applied to a rod holder per say. I think using these for a fish finder mount
only may be the best application when larger more powerful fish are involved. With larger fish, I think a flush or deck mount of some type like a Scotty is still the best way to go with a recreational kayak. In the end, these may be good for some applications but maybe not your particular situation.
Perry