So after http://www.thephotoforum.com/forum/showthread.php?t=98706 this thread I realised actually it may be worth just trying them out, and so I did, and so here it is, and I must say it works well. Does everything it says on the box. It's not super bright like the Nikon FE2 (probably blame the pentaprism not the screen), but the screen is a bit brighter than the Nikon FE but then so was my D200's standard screen. A few interesting points to note: - The katzeye screen really does work well preventing blackout of one hemisphere. It's not just marketing crap at f/6.3 with the DOF preview button I can still focus. - It works well in the dark, but ofcourse only as well as you can expect. That is to say I haven't turned into a cat that can see in the dark, but I can manually focus a bit darker than my digital camera can before it starts hunting, especially if the AF assist light doesn't reach the subject. - Reviewers talked a bit about extra "snap" in the ground glass which I passed off as a placebo of spending $100US, but while I wouldn't say "snap" I do agree it is easier to focus even when looking at the ground glass not the prism. - AF still works but that's a given since it doesn't go through the screen. - AE appears to be accurate and unaffected which was my main concern. I don't use any exposure compensation. - Installation was painless took me 5 minutes using a small screwdriver and a pair of tweezers, no damage, but then I am used to working with tiny surface mount electronics. The ham-fisted may want to send their camera in for this. One thing that was very interesting is that with the Nikon FE the prism itself was unaffected by focus. Meaning the subject would simply be split apart yet clearly remain in focus regardless of the position of the lens, (the ground glass of course rendered things out of focus). The Katzeye prism actually goes out of focus along with the ground glass which was a bit of a shock. I am not sure I like that feature yet. Mum loves it though compared to the Nikon FE. I guess it's just different. All in all what I am trying to say is it is highly recommended. /EDIT: Unfortunately I can't answer the question in the original thread. The optibrite treatment sounded like BS to me so I opted for an untreated screen.