Build Quality

Overall build quality is decent. When shaking the mouse, a very noticeable rattle comes from the CPI button. 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, unless the debounce time is set to 0 or 1 ms.

Buttons

Main buttons on the AJ199 4K are good. Pre-travel is moderate to high, whereas post-travel is low, resulting in a fairly firm and snappy button response. The buttons are visually separated from the shell, and lateral button movement is low to moderate when provoked. Button stiffness is medium. A pair of Huano switches (blue shell, pink plunger) are used for these.


Side buttons are very good. Both pre and post-travel are low on the forward button, whereas the back button has slightly more pre-travel, resulting in a snappy and pleasing button response. The pressure point is even across the entirety of these, though less so on the back button. Button size and placement are good, as actuation is possible rather easily by rolling one's thumb across. A set of Huano switches (green plunger) are used here.

At the bottom of the mouse is a single button for cycling through the set CPI steps, which feels fine. In addition, a simple slider switches between on and off-state.

Scroll Wheel

The scroll wheel is subpar. Noise levels are high, and tactility is below average, with steps mostly lacking clear separation. The encoder comes from TTC (yellow or "Gold") and has a height of 11 mm. The middle (scroll wheel) click requires medium force for actuation. Another Huano switch (green plunger) is used for this one.

Surface

The AJ199 4K has a 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 barely any signs of wear left after doing so. All in all, very good materials.

Button Sound Test

Disassembly

Disassembling the AJ199 4K is very easy. The screws are located beneath the rear skate. After removing those, top and bottom are easily separated, though some caution is advised not to rip the cable connecting the two.

The internal design is straightforward. The side buttons sit on their own PCB screwed to the top shell and connected through a 3-pin connector. The battery is stuck to the top shell and further stabilized by the side-button PCB. Everything else sits on the very thin main PCB, which is affixed to the bottom shell by no more than one screw. The MCU is a Nordic nRF52840, whose datasheet is found here. The Bluetooth capability of the chip remains unused.


As for the soldering and general quality of the PCB, I'm unable to find any noteworthy flaws. That said, I'm not particularly fond of the pins of the side-button PCB connector being soldered directly to the side-button PCB.