Some info for anyone interested:

https://www.steamgifts.com/discussion/RFMjj/humble-bundle-humble-killing-floor-bundle-25-aug-1-dlc-added-to-t2

https://steamdb.info/sub/482187/

Killing Floor 1 Bundle - $1 Tier DLC" (activates as "KF1 Humble Tier 1 DLC") is one key that activates the following:

Killing Floor - KF Gold - Ash Harding
Killing Floor - Chickenator DLC
Killing Floor - Robot Premium DLC Character
Killing Floor - Mrs Foster DLC
Killing Floor - Reggie the Rocker Character Pack

Thanks a lot! :)

Thank you~