Logitech barely touched a formula that already worked, and the two things it did change were exactly the right two things.
The MX Master line has been the default answer to "what mouse should I buy" for anyone doing serious desk work for the better part of a decade, and the 3S doesn't mess with that reputation so much as sand off its last rough edges. Same body shape as the MX Master 3, same MagSpeed electromagnetic scroll wheel that can free-spin through a thousand lines of a spreadsheet in under a second, same thumb wheel for horizontal scrolling. If you've used any MX Master in the last five years, your hand already knows this mouse.
The click is the first real change, and it's the one people actually asked for. Logitech swapped in quieter switches that cut the click noise by close to 90 percent by their own numbers, and in practice it's the difference between a mouse you can use on a video call without your coworkers hearing every left-click and one that still announces itself. I didn't think I'd notice this until I used it in a quiet room next to an older MX Master 3, and the gap is obvious immediately.
“I didn't think I'd notice the quieter click until I used it next to an older MX Master 3.”
The sensor jumped from 4,000 DPI to 8,000, which sounds like a spec-sheet number nobody needs until you're working across a 4K or 5K display, where the extra resolution actually shows up as smoother, more precise cursor movement rather than raw speed. On a standard 1080p monitor you won't feel the difference. On an ultrawide or a high-res external display, it's a real, if modest, improvement in how the cursor tracks.
Everything else carries over unchanged, and that's mostly a compliment. The scroll wheel still switches automatically between a ratcheted, notched mode for precise scrolling and a free-spin mode for flying through long documents, and it still reads the speed of your flick to decide which mode you're in without you ever touching a button. It's the single best scroll wheel on any mouse I've used, and Logitech clearly knew not to touch it.
Logitech Options+ software handles per-app button customization, and it's genuinely useful rather than bloatware you install once and ignore. I've got the thumb button set to Mission Control on my Mac and a different action entirely inside Photoshop, and the mouse remembers which app is focused and switches automatically. Setup takes ten minutes and pays for itself the first time you use it.
Battery life is rated at up to 70 days on a full charge, and that number has held up in my own use, closer to two months of daily eight-hour days before I needed to plug in the USB-C cable for a quick top-up. A full charge from empty takes about two hours, and even a one-minute quick charge buys enough juice for several hours of work if you're caught out.
The shape hasn't changed, which means the same caveat applies as always: this is a right-hand-only mouse, sculpted specifically for a right-handed grip, and there's no left-handed version. If you're left-handed, the MX Master line has simply never been for you, and the 3S doesn't change that.
At $99.99, it's not a cheap mouse, and the upgrade from an MX Master 3 specifically is a hard sell since the core experience barely moved. Coming from anything older, or from a standard mouse entirely, the quieter click alone justifies the price for anyone who works in an open office or shares a room with someone who can hear every click through a wall.
This is as close as a mouse gets to a solved problem. Logitech found the two things worth fixing and fixed them, and left the rest of a genuinely great tool exactly as it was.