Having done all the worktop joints for my kitchen, I'm bemused by one
thing. I don't see how the jig can possibly produce a perfect joint,
given that the female mitre will always have a different radius to the
male mitre, due to the width of the cutter.

I'm using the Screwfix jig. Do more expensive jigs have different
templates for the male and female joints that solve this problem? Even
having different internal and external radii on the 45 degree curve
would solve this, but the screwfix jig doesn't bother. I ended up filing
the male mitre a bit to get a better fit.

Ben