It's simply just sticks laid on <what> to create stops for different lengths for jumper wires which are then cut with flush cutters. This is still prototype so improvements might be coming in the future! It's ugly, but it works, so goal met here.
Addition: Afterwards i realized this jig is great for heathsrinks too.
Except for the yellow (0.4" ) jumpers that I bought a bunch of, I make most of my jumpers too. I don't like all of the different colors, so I stick to yellow. To help get the bent length right, I use one of these:
I then trim the stripped ends to be about equal. The ply I prefer to use is like the ply you show. It is often called Baltic birch in the US. It is considerably more expensive and has more plys than our common SPF ply (SPF = spruce, pine, fir).
I was going to say, you'll need to make sure the blade can handle it and that the wire you're cutting isn't too thick. I wonder if you ought to make your own blade out of a strip of metal you know will be strong enough. You could fit it into an old cutter.