I've used the little edge detectors from Fisher Machine for a few years now.
If I take my time and bump up 5 tenths at a time on the little CNC mills I
get pretty good results. Better than the machine itself. Good enough for
rubber worm molds anyway. I've never used the audible ones. No, not an
electronic thing, but a mechanical "click" when it breaks over. How good
are they? Does the mechanism that makes it click have a negative impact on
accuracy?

Also, is Fisher still making edge finders? I tried to visit what I thought
was their website and got a link farm page. I could have sworn I first
bought them direct thru Ebay then from their site, but I couldn't find
either. Just a few from third party seller.

One more question. How does a ball on a rod type wiggler compare for
accuracy to an edge finder? Seems to me that backing off and coming back in
slowly to get your final result would be kind of tedious with one of those.
My reason for even looking at them is because they kick so far back and up
when they hit that damaging crashes would be virtually eliminated.