The whirley blade smashes the bean to bits by rotating at high speeds. Powder clogs the filter, and boulders don't release all their potential contents into the brew. It is also difficult to reproduce the same results with the whirley blade. A better grinding method available to the home brewer is plate and burr grinding devices. Plate grinders clog easily but make fairly even grinds.
Burr grinders wear down eventually, but result in the most even grind in home devices.
The ideal burr grinder is a hand-cranked unit, like the famous German brand Zassenhaus models. I have had bad luck with electric models that need constant care and cleaning, and tend to break anyway. We think the Solis is the best burr mill out there. For example, a lot of people who like filter drip coffee try French Press and find there's too much sediment in the cup. You can use a Nylon Filter Screen and upgrade to a good burr mill, but you are always going to get a bit of turbid grinds in the cup.