It doesn't work with the Kinesis Freestyle2 keyboard, in case you were wondering. Damn, what the fuck did Kinesis do with this thing...? I haven't found any software able to manage the Fn key on this keyboard.
Edit: This seems to be because those are mapped to F14/F15 respectively in macOS by default. Apparently an non-Apple external keyboard cannot send Apples media keys, so unless your keyboard has its own media keys it will not work.
The Kinesis Advantage supports enabling media keys by pressing =n (see http://superuser.com/a/403765)