I'm not at home but I had one for the D100 and then bought one for the D2H/X. I believe they were the 4 and 5. If I'm correct the 5 is far superior. You can get 2x magnification and that's great when you're bending over. I'll check it when I get home tonight.
Yes, the DR-5 does have 1x & 2x magnication. It also has 90 degree detents so that it doesn't "wander" from the vertical (as the DR-4 did, as I recall). The DR-5 simply screws into the D2X eyepiece threads.