Karabiner and KMonad are great open source software. Don't forget to support the authors and contributors.
If you want to try home row mods on OSX, don't use Karabiner but KMonad.
KMonad is harder at the beginning but then it is easier than Karabiner.
Creating layers in KMonad is trivial and without drawbacks, while it is impossible in Karabiner without drawbacks.
You need to compile a PR of the project. Install https://github.com/pqrs-org/Karabiner-DriverKit-VirtualHIDDevice/releases/download/v2.1.0/Karabiner-DriverKit-VirtualHIDDevice-2.1.0.pkg