A few things come to mind:  the quality and consistency of the grind and the build of the grinder.  Makes a wonderful espresso.

Poorly designed chute - coffee hangs up in the burrs and in the chute.  Coffee grinds overshoot the pf.  This grinder makes a mess!!

I have been using a Solis Maestro with my Rancillio Silvia since July, 2002.  Originally, I bought the Maestro because I needed a grinder not only for espresso, but also for drip coffee (we now use a vacuum pot).  At the time, I did not see a reason for more than one grinder.

Since purchasing the Maestro, I have read about the differences in grinders and the many opinions on which grinder is best for espresso. My curiosity got the best of me and I decided to upgrade to a better grinder - one soley for espresso.  I considered getting the highly rated Mazzer Mini, but the price kept getting in the way.  Keep in mind, we are making only a couple shots of espresso a day.  Based on the many reviews and opinions I read, I bought an Innova Conical Burr Doserless Grinder (I-2).  I did so fully aware of the reported Innova shortcomings.  However, one attribute was consistent in the opinions and that  was the exceptional quality of the grind. Since that was the criteria for the new grinder, it was an easy decision.  Even easier when one factors in the price.

Let me make a few comments about the Solis Maestro.  I am writing this so that anyone else with the Maestro or someone considering the Maestro can benefit from my experience.  It is a nice  general purpose grinder.  One thing that is outstanding about the Maestro is the egress of the ground coffee.  There is no clumping and very little of the grounds are wasted - something I wish others would copy.  The Maestro is easy to clean and has a small footprint. What bothers me the most about the Maestro is the way the ring burr seems to be insecurely mounted.  It moves around too much - I don't think it should move around at all.  I don't know how this affects the quality of the grind, but it is unsettling.  Many opinions have pointed out that the Maestro is on the borderline of being acceptable as an espresso grinder.  After seeing the results of the Innova grinder, I have to agree.  One can use it for espresso, but it will not consistently produce a great shot.

The Innova is not perfect but it does produce an almost perfect espresso.  Since I am not making espresso shots all day long, I can live the imperfections.  It takes no longer to clean the Innova than the Maestro.  It does waste coffee.  It is not appreciably louder than the Maestro nor is it any slower.  It is bigger and heavier than the Maestro and seems to be better built. IT IS MESSY.  It is great for espresso but impractical for any other type of grind.  

Having used both grinders, I have to say the Innova produces an obviously superior grind.  I can see the difference in both the coffee grounds and the espresso.  The coffee grounds are consistent in size, light and airy.  The grounds tamp nicely.  The espresso is darker and has more crema.  The taste is softer and less bitter.  I could have spent more money and bought the Mazzer Mini, but I doubt the espresso would be any better.

My order was processed and shipped without problem.