I feel like a little kid asking all these questions but it's not like I have a bunch of buddies that do machining. In fact, I'm one of the few that know what end of a screwdriver works!
Anyway, I'll be looking at a DRO for my 8520 this summer, all three axis obviously. Now I've used DRO's a lot but I've never installed or bought one. Money is a bit of an issue since tooling up for my new mill is killing me and pissing off the wife a little. So I'll probably go with China glass....
Clausing 8520 Dro

Clausing 8520 Dro