I was careful in stating that I was referring to split screens purchased on EBay.
From my personal experience, I bought 1 of these low cost screens and installed it in an E-510. While, it was easy to install, and it did aid in focusing a manual focus lens, the exposure of my images had changed. To the point that I decided to take it out and replace it with the original screen. The exposure on my images returned to normal. I decided that it was better to go with the original screen.
Katzeye screens are a different product entirely and, since I've never used on, I can't really comment on it.