one that the mouse can see texture and thus know if it is being moved or not. A sheet of smooth glass is a bad pad for an optical mouse. But it can work well for the old mechanical mice that had a rubber ball that needed good traction.
I also have had a hard time using the MM on most surfaces like smooth wood desktops and mouse pads. I settled on a cheap thin plastic kitchen cutting board I found at a dollar store. It's about 1mm thick and flexible, 18x14 inches.
The MM uses two linear pads on the bottom and that might make it harder to move precisely compared to a regular mouse. Those pads make an annoying scraping sound on some surfaces.
I notice the MM moves very well on the smooth Formica-type table top they use on the Apple-supplied iPad and Mac display tables in stores like Staples and Walmart.