I also recommend focusingscreen.com's k3 split screen. I just installed it the other day and it works very well. Cost was 83$US plus shipping (cheap from Taiwan to Japan).
The actual screen was a Nikon product, fitted to work on the K5. It included all the necessary tools and shims, and instructions online were very good and detailed, covering all possible issues (front focus as well as back focus adjustment).
I now have no trouble focusing accurately using MF. You can use the green focus confirmation light in the OVF to get you close, and then fine adjust if you need to, using the split screen.
A couple of possible issues are focus shift, and loss of spot metering. For the former, make sure the lens you use to calibrate the screen does not undergo focus(focal) shift when stopping down the aperture from wide open. I have tested for the latter issue, and noticed no problems. Spot metering is still working perfectly.