Have you had an issue clamping materials and finding after the glue has dried, removing the clamps and your board were bowed. I know I have, no matter how I clamp with clams top and bottom and the heart of the timber taken into account there was always a bow. after a bit of research I came across a number of ideas all which showed prommiss. After a bit more looking around I came across a set of parallel clamps which clamped from the top, bottom and sides all to gether, but at just under $300 each I set about making my own.
If you want to make your own I am happy to put up some dimensions
My similar clamp, I just need to drill the Aluminium RHS and the bench top in a 96mm hole pattern (As well as make the bench frame and drawers and the downdraft baffle) I think the pins being undersized is what pulls the rails into compressing on the face, I think your style of clamp would put more pressure on the face.
These clamps apply pressure to all faces which gives good pressure to top and bottom, plus I do take care to ensure the heart of the material are oppsite ensuring little to no bow