I use Asus N550JK-DS71T with yosemite.
I just applied "Fn Brightness Keys Patch","Backlight PNLF-Intel-GFX0-Patch" and compile successful.
but it has one problem...
if press fn+f5, OSD shows slider down but display brightness get more bright.
and if press fn+f6, OSD show slider up but display brightness get more dim...