I installed a similar NEJE laser ("30W" with ~7.5W optical) and got it working easier than expected after reading all the forum posts. Maybe having the Duex5 was key as it just plugs into +/- of servo plug. The TTL Board that comes with unit has 3 modes when you push the pwr button: Off, Manual PWM via board buttons, and PWM-input-controlled.

I have been using Lightburn for Marlin with "inline" selected for "Laser Control Commands" to make gcode.

;Laser T6 Tool Definition
M307 H6 A-1 C-1 D-1; disable heater6 channel
M563 P6 D0 X3 ; Tool 6 Laser on U axis no heater or fan (change if on X axis)

Tpre setup:
M452 P6 R255 F10000 S1 I0 ; switch to laser mode Heater 6 PWM/servo to control the laser
M42 P6 S0 ; Ensure Laser Off
TFree setup:
M451; Go back to FFF 3D print Mode