I have been looking at these for a while but the price has put me off .
I acquired this bit of 20 mill alloy "jig" plate .
It should be ideal for the job , dead flat and square .
I went with 16 mill holes on 50 mill centers .
Bought some mole grip type welding clamps to modify .
Holy cra....... that's a nice plate....
Jig or "tooling plate" meant (at least over here) that it came from the vendor flat, very flat (IIRC .001 in 12")
That style need access to the the underside of the table to secure them so it is something to bear in mind with the overall design.
The ones that just slide in from the top like woodworking dog clamps could be more ergonomic for some jobs.
To increase versatility, some top hat bushes, threaded M12, M10, M8, M6 would allow the holes to be used with a standard mill clamping set.
Reaming the holes would allow stops to be put in them, so you can set up two fences at 90 degrees to each other. In the woodworking world, the Festool MFT works on a similar principles and is a source of ideas.