For the nerds on HN, the difference between a good grinder and junk is the consistency of particle size. There's an optimum particle size that will result in the greatest amount of desirable flavours being extracted; most cheaper grinders will spit out a wide gamut of particle size.

One of the most important jobs of a barista is to manage the grind fineness to optimise for the beans.

The reason that perfect espresso isn't made by a robot—the reason why the process is so variable—is because the source material (the beans) are volatile. They're constantly changing, each batch is slightly different, their properties change as they off-gas every day from when they're roasted, and they're greatly affected by storage and ambient humidity. Some of these variances can be compensated for by adjusting the grind.

It's not about grinders but it spends a few chapters on how coffee is produced and how different factors/regions can affect its flavor. It's an excellent primer on coffee in general, and of course on roasting at home (though the chapter on machines at the end is a little outdated).

In contrast, consider the Breville espresso machines. They make great coffee reportedly, but I understand they're next to impossible to service or fix yourself. I heard that a technician is required to merely clean it, much less repair it (maybe a machine owner can chime in).

So I guess you gain some and lose some with economies of scale and espresso machines.