Nicky:

The Incra positioner, and Wonderfence, is probably well-suited to the precision work you do (guitars).
The Wonderfence is an acquired skill – very precise; however, there are many adjusting points; and you do need to be mindful of the fence’s internal edges when you get the bit inside the split-fence halves (spin the bit by hand after you lock down the fence, to ensure that the bit spins freely).
I’ve abused mine for many years; and I believe that the Incra user community, at-large, is quite complimentary of the products.
If you are so inclined, call Mark Mueller at Incra – he’s the guy you see on all of the videos, and is head of their Customer Service or Sales Support function. He’s a very user-friendly person – he’ll address any and all questions on applications.
MJCD