The K10D's focusing screen is smaller than the *ist series' focusing screen. I think that's why you don't need the shim. I know for sure that the K10Ds focusing screen is smaller because I tried to cut a focusing screen for a K10D using an istDL template, and it won't fit.
I don't have the Katz focusing screen, but I bought one from jinfinance of ebay and put it on my DL and can not be happier. It does change the metering a 'lil bit and I compensate with -1/3EV.
For the K10D I cut the focusing screen from pentax m focusing screen, the one with split prisms and collar. I also put grid lines on it. Both focusing screens are really great helper to me.
Originally Posted by JJJPhoto
I'm pretty sure several other people in this forum have purchased split prism screens from this ebay seller as well. The one thing I'll mention is that I didn't need the "shim" included with the screen when mounting the cheap screen in my K10D, but I had to use the shim when I mounted the cheap screen in my DL. I just thought I'd mention it so you don't throw away the tiny U-shaped shim that comes with the screen if you purchase the screen from the ebay seller (you might need it) depending on the camera.