[iramiller]

A good burr grinder is all about consistent grind size and is very easy to observe.

Spread a small amount of ground coffee out on a piece of paper. Observe the varying sizes and shapes within the grounds. Better grinders produce more even grinds which produce more even extraction during brewing.

It’s an exceedingly simple concept. As an extreme example try and brew an espresso using a simple blade style ‘grinder’. It will be impossible. The refinement of a good grinder is simply optimizing along this axis.