The SKR and MKS are cheap, poorly-implemented, mostly-unsupported rip-offs of the Smoothieboard, and don’t have the same more powerful hardware that the Laserboard offers. See here for more on MKS:
The Laserboard is also based on the Smoothieboard, but unlike the Chinese companies, Ray gives credit where credit is due and contributes back upstream. He stands behind his product and takes the time to assist folks with problems - personally - here on the forum.
The Laserboard has some custom features and optimizations intended purely for laser use, taking Ray’s years of experience with these machines into account. It has protections and conveniences that you won’t find on a stock Smoothieboard. The Smoothieboard (and the MKS/SKR, for that matter) was designed largely for 3d printers and CNC routers, with laser support tacked on because it was “easy” to support in software. But, it doesn’t have many of the same protections against the hostile electrical environment inside a cheap CO2 laser. Ground isolation, protected inputs/outputs, FET switches - really, everything was thought of to make it as compatible as possible with as many machines as possible.
The stepper drivers are upgraded to Trinamic TMC2224 units, which are (in my opinion) superior to the A5984s on the Smoothieboard.
Perhaps the best feature, though, is it’s a drop-in replacement for the M2nano and Moshiboard found in many of the cheaper K40 lasers. I’m not sure what the full spectrum laser you are interested in has in it, but if it’s an M2nano, it will be very easy to integrate with the Laserboard. Even if it’s not, it will be straightforward to convert whatever it does have over to the Laserboard.
Really. It’s worth the extra money. You’ll end up wasting at least that much in time and materials with the other options.