The Wadkin mitre fence that came with mine is nothing particularly special. You're not missing out on much!
As a side note, are you folks using the original main fence on your AGS10? Mine has the front and rear clamping design which I find to be a bit hit/miss. I'm looking for something more modern/functional.
I have the front and back style fence on mine.
My whole saw is a collection of bits as the courier dropped my first one, and the fence was smashed.
I accquired an ags250 fence and rail (same as fitted to the last of the ags10) but then accquired a front to back fence as well, before I had a chance to fit the ags250 one (which required drilling the side of the table for screw holes)
The ags250 is said to be a far superior fence but, really, I've found no real issue with the front to back one.
The scale is all in Imperial and I always have to think a bit harder than I'd like when using it, but if I need it accurate, I make a test cut and measure, and then adjust.
For work I cut metal. I can get to within about 0.05mm of intended dimension with care. What's that in old money, about 2 thou?
The wadkin isn't on that level but I'd say I can keep to within 0.3 or so of intended if I pay some attention, possibly even better.
Nothing is perfect. On a CNC mill the cutters ware constantly so the dimensional accuracy is always changing. It's about realising evreything is moving and reclaibrating as often as is needed for the degree of accuracy that you need.
I'd say the same about the wadkin fence really. I don't pay any real attention to the scale on the fence, but just adjust to the work that I need.
That's my take on it anyway.