Jim: I have age-related visual acuity issues (sharpness of vision). Here are my experiences with manual glass (most of my lenses are manual).
My experiences are with the 70's and 80's cameras, as you can see below. SP-F and KX = micro-prism. K2DMD and MESuper = split-image. KX is my favorite camera, closely followed by K2DMD and MESuper.
Focusing is really just practice and learning how the camera works, as well as using a particular camera / focusing screen for its strengths. Match your camera strengths to your intended shooting style (or particular need for an outing - perhaps have more than one camera, each for a purpose - the MF bodies are so inexpensive!!)
- Take your time, whether autofocus or MF. I have had to give up most fast-action MF photography - so what?
- Split-image reticules help a lot, but at smaller apertures tend to black out - fast lenses black out at larger apertures than slow.
- ME/MESuper/MX have bright (brightest?) VF, permitting somewhat slower glass, thus allowing use of the split-image at smaller apertures.
- Using smaller apertures and faster film (or slower shutter) allows a larger depth of field and some focusing "cushion." (kind of a zone focusing effect).
- Can be an issue for macro if you want wide apertures for bokeh, but you would use spilt-image for this).
- Certain lenses have a more pronounced "snap" into focus than others, but with practice you will come to recognize the "snap into focus" as you rotate the focusing ring. Example in my bag is the Tamron AD-2 SP 90/2.5 Tele-Macro #52B - has a very visible "snap"
- Using the micro-prism just takes some practice and some note-taking when using film so you can select the keepers (and failures) and refer to what you did - learn to do what works.
One unexpected advantage to K20D is you can practice for "free" with the matte screen - so what if you throw away 100 images? - and use gained skill for film cameras.