I use dividers. They can be adjusted for any spacing you want, coarse, fine, or in between. For most of the leatherwork that I do, I use five stiches per inch, so I set the points of the dividers 0.200" apart, and "walk" them along the seam. It helps if the points are sharpened, and on rougher leather you need to exert more downward pressure to make a visible impression.
The dividers are infinitely adjustable. If the length of the seam doesn't come out even at the spacing of your choice, the dividers can be adjusted in or out very slightly for marking the last four or five stitches, so you end up where you want the end to be, and the minor change in spacing is virtually invisible.
I never could work with the stitching or "overstitch" wheels. I simply could not get them to work satisfactorily for me. I'm just an amateur, though.
Good luck with your project!
Notchy Bob