Logitech barely touched a formula that already worked, and the two things it did change were exactly the right two things.
My MX Master 3 started shedding its rubber side grip after four years, in flakes, onto the desk, which is the only reason I looked at the 3S at all. The line has been the default answer to what mouse should I buy for serious desk work for the better part of a decade, and the 3S sands the last rough edges off rather than touching the formula, so it's the same body, the same thumb wheel, the same everything your hand already knows if you've used one of these in the past five years. The two changes are a quieter click and a sensor bump from 4,000 to 8,000 DPI.
The scroll wheel deserves most of this review, because it's still the reason to own the thing and almost nobody frames it that way. MagSpeed reads the speed of your flick and switches between a notched, ratcheted mode for precision and a frictionless free spin that crosses a thousand-row spreadsheet in about a second, on its own, with no button press and no wrong guesses. I've used this wheel daily across two generations of it and it has never once changed modes when I didn't want it to, which is not something I can say about several mechanisms in this house that cost a hundred times more. When somebody asks why anyone pays $99.99 for a mouse I don't bring up the DPI at all, I hand them the mouse and tell them to flick the wheel, and that has worked on everyone I've tried it on so far.
“I hand people the mouse and tell them to flick the wheel, and that has worked on everyone I've tried it on so far.”
The quiet click works as advertised, cutting click noise by around 90 percent per Logitech's own numbers, and next to an older MX Master 3 in a silent room the gap is immediate, so video calls no longer feature my left hand as a percussion section. My confession is that I miss the loud click a bit, because a click that clicked felt like the mouse agreeing with me, and the new one is polite and correct and better for everybody I live and work with. For about a month I opened the drawer with the old mouse in it once a week just to click it a few times. The 8,000 DPI sensor shows up as smoother tracking on a 4K or 5K display and you won't feel it at all on a 1080p monitor, which is the entire story of that spec.
Options+ justifies its install for once, since my thumb button is Mission Control on the desktop and a different action inside Photoshop, switching over automatically with app focus, and the ten minutes of setup have paid rent every day since. Battery has held near the rated 70 days in practice, with a one-minute top-up buying hours. It remains right-hand-only and sculpted for that grip with no left-handed version, same as it's been since 2015, and I couldn't find any reason given for that anywhere beyond people assuming it's the tooling cost. Owners of a 3 have a weak upgrade case here and everybody else is buying about the closest thing the mouse world has to a solved problem. The old mouse is still in the drawer, and I've definately stopped pretending I'm going to throw it out.