Call me old-fashioned, but I take the traditional approach to manual focus. On early cameras (bellows cameras with no focus other than manual focus) the focus control was calibrated (and I use that term loosely) in either feet or meters and was quite adequate - then and now.
The trick with manual focusing is to "guess" how many feet it is to your subject. Most people are very good at guessing distances up to about 20 feet. Beyond that, it makes very little difference, because for normal lenses the scale gets very compressed beyond 25 feet.
The other trick with manual focus is to take advantage of the hyperfocal distance. In other words, when in doubt, put your focus setting at a value such that the extreme hyperfocal distance for your particular lens opening sits right on the infinity mark. In that way, you have a point and shoot setting that will get you through almost anything except macro work.
When I was a film photographer with my AE-1 bodies and a normal lens, I would always put my camera to the ready by manually setting the opening, shutter speed and focus for the most general situation. Using the hyperfocal distance settings was easy because the lens barrels of Canon lenses had those hyperfocal distance marks right on the lens for each aperture.
