I added a cheap Chinese laser, 5W. I tried something a little different - a chunk of picatinny rail on the side of the router mount. So far, working well, could use a little paint but otherwise good. Easy to remove. Having trouble with some interference from something causing the board to reset when I use high power on the laser, but I suspect it’s a wiring routing issue of some sort.
I’m using a SuperGerbil board, which has separate outputs for flood and mist cooling. I’ve hooked up “flood” to a SSR that controls the power supply for the laser. This lets me enable the laser via gcode separately from the router (which is enabled from pwm), so I don’t need to change anything significant with respect to my router control via pwm->an IOT switch (which I may just replace with another SSR) - I can just plug in the laser, turn off the router, and have separate power control for the laser without a switch.