Got it, took a few "test" photos, been using it a little. I've been planning on a proper write-up but haven't dumped any photos yet.
At this point, I'm still trying to decide a couple things... like if it's showing focus at exactly the right place (sometimes you need to play with shims or such to get it absolutely perfect; they will do this for you if you send them your camera and pay extra), and so far I'm mainly only used it for very challenging things: like taking photos of Jack from fairly close with an F1.2 lens! Between the constant movement, the lack of contrast (with his face taking up much of the frame), and the extra tiny DoF of this lens, it's tough to nail focus consistently, and the lack of contrast doesn't really show the usefulness of the split-image/microprism.
Also, I'm not such a fan of the split-image in general. My K1000 that I've used for years has only a microprism grid and that's what I'm used to. I recently picked up an older K1000 that has only the split-image and I find it much trickier to use. I'd probably like the Katz-Eye the best if it was microprism-only. Maybe I'll have to try one of those cheap $30 eBay screens.
Don't get me wrong, though, I
think that I really, really like it though; I just want to make sure that it's set up to give me exactly the right feedback, otherwise it's really no help. The couple times I've tried focusing on static objects, it seems pretty good; it's certainly much easier to tell when you're nailing focus as long as the object has at least some contrast.