I recently bought the Next Gen Standard 2.5" mill. I followed the instruction to let the weight of the top piece do most of the work.
However, because the milling chamber contained flower pieces of varying size, the milling top didn't rest evenly on the material, and wobbled uncontrollably as I turned it. I learned to hold the top piece level and in contact with only the biggest piece of flower, then twist back and forth in short, quick strokes. As the remaining volume of material goes down, the top piece contacts more and more of the flower, and suddenly it goes (gently) aground on the mill plate.
The result is a very fluffy "grind," with 2 problems:
1) Some stems get through the milling holes, which are larger than I expected (it's not replaceable on this model).
2) The "grind" is a bit irregular, and not quite fine enough.
I found that I could run the milled flower back through the mill again, once or even twice, and pick out the stems I see along the way, the result is finer, more consistent, and still very fluffy. This works great for me.