Hey Floris! My monitor is a Dell U2715H with an GTX970 (Asus) with NVIDIA Web Drivers enabled on Sierra 10.12.2. So far you're app hasn't KP'ed or made my system unstable. I would LOVE, to have the brightness keys control the brightness. Or any other keys for that matter, because I can imagine that you can't use the brightness keys in Xcode due limitations.
If you need help beta testing, PM!
I think a well packaged app will be a life-saver for the community and it could be really big instead of being down somewhere in the forums. Maybe you'd then get some help from other developers also to make it more stable with more combinations of hardware