I fitted one to the cross slide of a CVA lathe some years ago, actually it’s still fitted but I don’t use it.
Repeatability is quite good but accuracy leaves a lot to be desired on a lathe due to everything being doubled because of removing material of both sides of the job.
BW say they are good to 0.002″ but that, on a lathe, is 0.004″ on diameter.
Whilst it helps to keep an eye on things it’s best to measure and go the final position using the dials.
I fitted a DRO to my TOS lathe later on and went the glass scale route for about the same money and have never regretted it as this can be used without dials very accurately.
However glass scales may not fit easily on a smaller machine as well.
Personally for the day I think they were very good value but the BW units have increased in price just as the glass scale units have decreased in price and it’s now a very hard choice of price versus features versus size.
John S.