Full-sized form, switched to it after the m310 (caught a double click after a few months of work) which is slightly smaller but larger than most other laptop mice. And I don't recognize the smaller one.
A pair of side buttons back and forth, it's really inconvenient to work without them.
A wheel with a side scroll, besides, its functionality can be reassigned.
The rubberized sides of the mouse prevent your fingers from slipping too much while holding.
Pleasant rough plastic at the main working surface of the mouse (I hope it will not wear off over time), not easily soiled.
An optical sensor (in new revisions, optics, not a laser, as they say everywhere!) Without obvious signs of terrible acceleration (but still there) and (most importantly) without strong angular binding (but it is also there, just not as annoying as in other office mice )! In general, this gives more freedom in cursor control than on the same m310 or others. However, this sensor is not suitable for games, except for casual players. For God's sake, turn off this "increased pointer precision" on your system.
A long service life from a pair of batteries (a couple of years withered), while the mouse may well work from one. Why it was necessary to fence a garden of two is not entirely clear to me. Moreover, one drawback follows from this (more on that below).
unifying receiver. Those who have a whole bunch of devices from Logi will appreciate them.
The presence of software for reassigning the actions of all functional mouse buttons.
Just a comfortable, symmetrical shape. Suitable for left-handers and right-handers, but full functionality is still for right-handers due to two side buttons for the right hand.
Good Teflon legs (otherwise sometimes they put such slag), although so that they serve for a long time and the mouse always glides well and evenly - buy her a simple rug.
Nice clicks. The click is clear, informative, with a good return, without overtones. The same pressing force in different parts of the upper plate.