I ran a modified digi caliper on my lathe cross slide for a while, but found it really achieved nothing. I work mostly in metric on an imperial lathe and conversion is easy as 2 x table (0.1 mm requires 2 thou on the dial). Eventually it had some problem (cant remember now) and I couldnt be bothered to repair it.
What I do have is a long Arc Euro magnetic bar on the long axis. A very worthwhile mod.
I value the advanced features on my 3 axis Sinpo system on rhe mill, but really don't see that I could justify the expense on the lathe.
Martin