Not OP but using the mx ergo since more than a year. Never really had problems with the precision, the precision in the first week of using the mouse will definitely be different, because your brain needs to adapt. The only time I have problems is, when I haven't cleaned the trackball for some time, then it will get jittery. But the mouse has a precision button next to the trackball where you can move really slow and will definitely have a chance to move just a few pixels.

There’s a dedicated button right at your thumb that increases precision on demand. :)