I have not played around with an electron microscope in probably 25 years. You don't see them used as much these days as other molecular tools have supplanted its utility. I still do use those cool tweezers though
My statisticians would tell me that the key statement in this report is "I cannot guarantee that these are representative grind samples" You can get a general impression as to the grind variables between samples but that's about it. The EM samples also require drying if I recall (the chamber is under vacuum - correct?) so that most certainly will affect what you are visualizing.
I would guess that a simple dissecting microscope with camera taking freshly ground samples in normal temperature and humidity ranges would be more representative of what you put in the basket from each grinder.
Just another mad scientist's view.
Edit - I just looked through John Weiss' particle size review and that was cool and well controlled. Nice work.