It's a 3rd party MMU. There isn't much documentation so you're kind of on your own setting it up which is a pain, once I got it figured out it runs very smoothly though.
I just permanently leave for spools loaded up with my most common colors, even if I do a single print I'll just use the mmu code so I'm not swapping spools for every print
It's a bit of a project but I can share my code which will give you a huge head start. There are good amount of people using it on a K1 too
The code the creator gives you is not great. It forces you to use filament 1 first even if it's not present in that print. I fixed that and other things, made it swap colors 4x faster
If you have no plans of getting another printer and love your K1 I think it's a great idea to just put an mmu on it