In addition to the Maestro, I have a Pavoni Zip and and recently sold my Rocky. The Pavoni is obviously a commercial workhorse and works like a champ for my e61 ECM Giotto. I picked up a used Maestro from Craigslist to hold me over for a week until my Pavoni was operational again with new burrs.
The Maestro "barely" worked with my e61 ECM Giotto. The Maestro has its limitations in that the grinder has really one usable setting for an espresso grind. I would then have to adjust my tamping to get me close enough to a 25s espresso pull. Even with one setting, I noticed the setting had lots of play so the grind was somewhat inconsistent, which resulted in some channeling of my espresso shots. Moreover, there was lots of static clumping of the espresso grind, but I was able to eliminate the clumping by using a bamboo bbq skewer to break up the clumps before dosing. The other major drawback is that the Maestro would take a significantly long time to grind a single serving of beans since the conical burrs are tiny and sometimes would get jammed since the nozzle from the grinding basket is very small. Given that I was used to my Rocky, which worked like a champ for my Silvia machine, the headaches of slow grind time, constant jams, inconsistent grinds, clumping of the grinds, the Maestro was "barely" working for espresso use and thus not a realistic long-term solution for me. Since my Pavoni was operational again, the Maestro is now my drip and french press coffee grinder, which works perfectly for this application.
In terms of quality the grinder is mediocre. I am not sure if it is because it is used, but I felt build quality to be somewhat be cheap. Everything on the exterior is made of plastic which has some flex, the knob keeps on falling off every time I twist it to turn on the grinder, and the grind setting when you twist the hopper has a very loose feel to it (which results in inconsistent an espresso grind). Again, I am comparing it to a Rocky which feels like a tank since it is made of mostly steel, with the exception of the hopper. As for usability, it is extremely easy to figure out how to use. Twist the hopper to set your grind setting, poor in your beans, and twist the knob to turn on the timer for the motor. Although the grinding chamber is small and takes a long time to grind a serving of beans, the benefit is that you don't waste much beans when you are adjusting the grind settings or trying to flush out old beans/grinds from the time you used it before like you do with a beefier grinder. The Maestro is incredibly quiet and is very small and light. The former user told me the Solis customer service is excellent since he had the hopper replaced free of charge.
For a primary grinder, I am not sure if I would get one brand new. I think I would pay a little more and get a used prosumer model instead to have the extra flexibility of being able to support a usable espresso grind. If you are looking for drip and french press it works great and much better than the Costco Cuisinart burr grinder, which I had several years back until it broke on me.