Build Quality

Overall build quality is solid. There is a rattle when shaking the mouse. When applying lateral pressure, minor creaking but no flexing of the shell can be observed. Activating the side buttons by squeezing the sides is only possible by applying excessive force. Lastly, accidental clicks when slamming down the mouse do not occur.

Buttons

Main buttons on the M991 Enlightenment are good. The left button in particular has significant pre-travel but low post-travel, whereas the right button has less pre-travel but more post-travel. In terms of click feel, the left button is more muted than the right one, which is sharper and more defined, yet both are quite snappy. In addition to that, the right button is slightly squeaky. Button stiffness is light (pressed towards the front) to medium (pressed towards the back). A pair of Huano switches (blue shell, white plunger) is used.


Side buttons are decent. Both side buttons have significant pre-travel, with the back side button being the greater offender, whereas post-travel is equally low on both. Button response is firm and pleasing. The pressure point is far from even on the back side button in particular. The front side button has a dot pattern, which makes it easier to tell the buttons apart by feel. Button size and placement are good as actuation is possible rather easily by rolling one's thumb across. A set of switches from CF (red plunger) is used for these.

At the top of the mouse are two buttons for cycling up and down through the set CPI levels, accompanied by a third button which cycles through the available polling rates. Their click feel is good. Another set of switches from CF (red plunger) is used here. An additional button can be found next to the left main button, which too feels fine. The switch comes from Himake (white plunger). At the bottom of the mouse is a slider for switching between off-state, on-state, and "eco mode," which disables lighting. Furthermore, a "mode switch" button can be found there, which switches between two on-board profiles.

Scroll Wheel

The scroll wheel is good. Noise levels are mostly under control, but tactility is severely lacking as the individual steps are barely perceivable, resulting in very light scrolling. The encoder is from F-Switch (gray, black core) and 13 of mm tall. The middle (scroll wheel) click requires high force for actuation. Another switch from CF (white plunger) is used for this one.

Surface

The M991 Enlightenment has a smooth matte surface at the top and patterned sides. The former does attract fingerprints, dirt, or the likes quite readily. It is easy to clean, and there are barely any signs of wear left after doing so. All in all, decent materials.

Button Sound Test

Disassembly

Disassembling the M991 Enlightenment is fairly easy. First, all the skates and the screws beneath them ought to be removed. Once those are taken care of, top and bottom shell can be separated with ease.

The internal design is quite simple. The top and side buttons sit on their own PCB screwed into the top shell and connected through a 6-pin connector. An auxiliary PCB next to the scroll wheel provides wheel illumination and is connected with a 4-pin connector. The battery rests atop the recess for the wireless dongle. Everything else sits on the main PCB, which is moderately thick and not affixed by any additional screws, whereas the side-button PCB is quite thick. The MCU is a CompX CX52810. From a design standpoint, there is no apparent reason for not centering the sensor.


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