I spent a fair amount of time shaping a crochet in walnut that looks like ones I have seen, more or less resembling the profile of a human hand. Held it up to the bench and decided I didn't like it aesthetically or functionally, so decided to start over.
As I thought about it, the crochet is nothing more than the vertical analogy of the planing stop. On the Nicholson bench, that is simply a square block of wood. It doesn't hold the workpiece down to the bench; gravity does that. When you plane the edge of a piece held vertically against the sideboard, holdfasts hold it up and against the sideboard. As far as I can see, all that is needed from the crochet is to function as a planing stop, nothing more. If you make it wrap around the workpiece, it sticks out too much for my taste, limits the thickness of the piece you can hold and doesn't seem to serve any purpose. Anybody know why crochets are the way they are?
I spent a few minutes creating a basic planing stop as an experiment, bolting it to the bench in case I end up not liking it and want to remove it. I think it fits the look of a Nicholson bench very well and functions perfectly. The picture below shows my first effort and what I ended up with. It works great. It obviously doesn't need to be 2" thick and I may make a thinner version 2.
Once you edge plain on the front of a Nicholson bench you'll wonder how you ever did without it. It's a horizontal workbench. Tremendous.