Shaggy,

in my opinion too many things can go wrong when checking infinity with a ground glass - for amateur use. You as a professional repairman know what your are doing and thus you act - but the now and then repair hobbyist (as I am one ;-) would leard the hard way... and I did, I couldn´t trust my Moskva5, my Adox Start, my Agfa Billy 6,3 until I aligned them with the fathom collimator method.

What can go wrong?

- too coarse grain in the GG
- wrong size, wrong position, wrong side up front
- judging the sharopness is highly subjective - it depends on your eyesight and a personal jugdment ("It´s sharp... NOW!").

With the collimator method you´ll see a straight line for a moment and this is the position to stop - the microprims/indicators on the SLRs ground glass make that easy to judge. With a very low margin of errors.