Hi, NiLuJe, I agree the
six-inch Aura has an odd screen -- flush with bezel, supporting pinch and zoom for font sizing, two-fingered mid-screen swipe to control brightness.
But that's not the model I'm talking about. 
I'm talking about the
Aura HD, with, as I said, a
6.8-inch screen.
I've used the night-mode hack on both models (
Kobo Aura 6-inch and
Kobo Aura HD 6.8-inch) with perfect success since 2014. It's only with recent firmware that I'm having trouble with the devmodeon method, and only with the
Aura HD (it works flawlessly on a regular six-inch Aura).
(I am a Kobo beta tester, by the way, but my
Aura HD is not in the beta-test-release stream.)