So I have been able to compare now having received the Katzeye screen. In short, while the split prism and micro-prism ring do work accurately, the matte area of the screen is barely an improvement over the stock Pentax screen.
Unfortunately for me it was the matte area I really want to get back to how it was in my film SLRs, since the place I want to focus is not always right in the middle. For my film cameras that I used daily I have all-matte screens with no split/micro prisms at all (to me they just clutter the view and aren't necessary on a real focusing screen) and for snap manual focusing, focus and frame in one movement, these have always been great. Some later AF film cameras had all-matte screens as standard (with AF marks) that work just fine for manual focus. The prisms are useful if you have eyesight issues or for some specialized applications. But for the kind of shooting I enjoy, a real focussing screen should not rely on the prisms at the centre to be accurate or fast.
What I would like is an all-matte screen with the sharpness and clarity that the ones in my film cameras have.
In summary... The Katzeye is an improvement over the Pentax screen only if you specifically want the split and micro prism features, it works great.
If you want a sharp focusable matte area on par with a film SLR its barely any improvement and not worth $150.
Outcome, for the quality of viewfinder I am used to (from film SLRs) I will have to keep on using my film SLRs. Next experiment is a full frame body and a screen upgrade for that. Used FF bodies are getting very affordable so it's not a prohibitive experiment anymore.
I rattled on more about it at
Photographen.co — Katzeye focusing screens; do they work?
Thanks everyone for your feedback. Hope my experience might help someone else down the road.