Modern DRO kits are pretty incredible.  When I bought my mill, someone had removed the Heidenhein glass scales.  If you aren't aware, Heidenhein pioneered glass linear scales, I had used a lot of them in my previous job and would have loved to replace the ones on my machine, but I was able to get the entire system for probably 10% of the price and haven't had a single issue.  The new kit was actually a step up as the original readout was just DRO, but the new one has things like hole circle calculation, which saves time and reduces human error.