Great; glad you are joining the project!
You can see each layout and key set on the Full Key Set page:
https://www.modelfkeyboards.com/product/extra-set-of-brand-new-production-xt-quality-one-piece-keys/
You can also do an online search for “German Model M keyboard” for example to see what it would look like. The F122 would have 10 extra keys on the left side and 12 extra keys above the F1-F12 function keys, that can be filled with keys on the extra keys store page:
https://www.modelfkeyboards.com/product/new-custom-legend-keycaps/
“Use your own keys” allows you to use original buckling spring Model F or Model M keys or Unicomp keys. MX and other keys are not compatible.
