Build Quality

Overall build quality is solid. When shaking the mouse, a minor rattle comes from an indeterminable location. When applying lateral pressure, minor creaking but no flexing of the shell can be observed. Activating the side buttons by squeezing the sides is impossible. Lastly, accidental clicks do not occur when slamming down the mouse, irrespective of what the debounce time is set to.

Buttons

Main buttons on the M42 Wireless are excellent. Pre-travel is low and post-travel low to moderate, resulting in a firm and snappy button response. While the buttons are visually separated from the shell, lateral button movement is minimal and needs to be provoked. Button stiffness is medium. A pair of Kailh GM 8.0 (80 M) switches are used.


Side buttons are very good. Pre-travel is low on both buttons, but post-travel is noticeably higher on the back button. Button response is pleasing regardless. The pressure point is even across the entirety of these. Button size and placement are good, as actuation is possible rather easily by rolling one's thumb across. A set of low-profile switches from Huano (white plunger) is used for these.

At the top of the mouse is a single button for cycling through the set CPI levels. Its click feel is good. Another low-profile switch from Huano (gray plunger) is used for this one. The slider at the bottom switches between off-state, CPI control, RGB control, and the PGDN bind. While fairly stiff, this slider also works just fine.

Scroll Wheel

The scroll wheel is good to very good. Noise levels are elevated in general and scrolling up gives off a grinding noise in particular, but tactility is good, providing clearly separated steps and controlled scrolling. The encoder comes from F-Switch (brown, pink core) and has a height of 10 mm. The middle (scroll wheel) click requires high force for actuation, yet another switch from Huano (blue plunger) is used here.

Surface

The M42 Wireless has a smooth matte surface all over. Grip is fine, and it doesn't attract fingerprints or dirt too much. It is easy to clean, and there are no signs of wear left after doing so. All in all, excellent materials.

Button Sound Test

Disassembly

Disassembling the M42 Wireless is fairly easy. First, the front and rear skates, along with the screws underneath them need to be removed. The sides are additionally locked in with clips, which can be hard to dislodge. When doing so, make sure not to rip the cable connecting the side-button and main PCB.

The design is reasonably efficient. The side buttons sit on their own PCB screwed into the top shell and connected through a 3-pin connector, while an auxiliary PCB next to the scroll wheel secured with two screws and slotting into a connector on the main PCB provides wheel illumination. The battery is glued into a plastic encasing sitting atop the sensor, which can be moved and fixated by two bottom-facing screws accessible through the bottom shell. All PCBs are very thin to save as much weight as possible. Three screws in total are used to affix the main PCB to the bottom shell, including one hidden below the diffuser at the back, which serves no real purpose. Inexplicably, the PCB also has a "PMW3370" marking on it. The MCU is a CompX CX52850.


As for the soldering and general quality of the PCB, I'm unable to find any noteworthy flaws.