Karabiner is an open source software and you can use it without any purchases.
You can pay software fee via PayPal to support this project.
(It's nearly a donation, but we can not receive a donation by Japanese law and the constraints on government regulation. Thus, it has taken the form of software fee.)
We does not provide any difference between purchased users and not-purchased users.
Please pay if you are interested to support this project.
I appreciate all donors. I received your donations!
I'm afraid I don't have enough time to reply for donors.
(I'm giving priority to develop Karabiner-Elements at the moment.)
Feb 1, 2019