The triangle shape should be a little less sensitive on how well the wire is connected / soldered. It could also make soldering more easy, as heat is not conducted away so fast.
when I build it, I plan not to use any wire or solder and directly screw on the binding posts
I made this purely by hand: hand cut, hand drill, hand soldering, without any measurement of geometry when make, symmetry done by eyeball observation only, no adjustment/trim of any kind afterwards.
Thickness of the triangle copper is 1.5mm, length of each side is aprox. 21mm, diameter of the copper bar is 2.2mm, diameter of the wires is 0.8mm.
When I run thru a current of 6.2A into 2 wires of any of the 6 combinations(excluding reversal), I measure the other two wires with less than +-0.3uV voltage variation with my 34401A.
This means that I have achieved the kind of zero that OHM-LABS claimed in their specification just by this simple DIY.