If i could tell you to pick a grinder this would be it. Ive sold many of these over the years and never found anything other than top performance. These grinders last forever and are constant with high volume.
 
From Mahlkonig
 
The K30 Vario Air features our proven espresso grinding technology and active cooling to handle high daily workloads. This classic is equipped with the grind on demand principle for hands-free operation, programmable push buttons for single and double doses as well as with a stepless grind adjustment to ensure for the perfect setting to match your espresso beans.
 
Grind on demand: Fresh aroma-saving portion grinding directly into the portafilter
Hands-free operation: grinder starts automatically when inserting the portafilter
Precision burrs made out of wear-resistant steel
Stepless grind adjustment
Electronic controller for exact and consistent dosage
Electronically controlled ventilation for higher daily workloads and cooler grinding
Push buttons for single and double-shot dosage
Red Dot Design Award winner
Illuminated display