QueenBeeSo to merge these two statements. QMK is common, and very powerful, and very well documented.
https://www.gitbook.com/book/qmk/firmware/details
However, with power comes complexity, in both usage and setup.
There is an easier way to do it if your keyboard is supported: http://kbfirmware.com/
You just use KLE and upload your KLE raw to that site. Not sure if it works for KBD75 though, but there are several guides out there for it.
I'd rather use something QMK based than the easy to use proprietary options at this point, honestly.
ChuckDeeQMK's gitbook is excellent and has a very detailed guide on how to install, setup, define a layout, create macros, and generate a .hex file.
I had more trouble flashing the firmware to my pro micro (up until I found out a workaround) than modifying a keymap, defining my own string macros that are on multiple layers, and generating the .hex file.
ZambumonYes, I found that to be true, which was why I linked it. However, the windows portion is in its infancy, and the docker portion has the same problem. I was able to get Skully to compile it for me in the meantime, and I continue to attempt in my spare time, which I have very little of. As I said, with power comes complexity.
Remind it before you purchase one.