Where are your Super and Fn keys supposed to go?
For Mac on this layout, it would be Control (1.5u), Alt (1u), Super (1.5u), Space bar (7u), Fn (1.5u). One could use the right most 1.5u for another Super as well.
I use all the OS's, but for work I generally use Mac, which is common among developers and designers.
The layout isn't the worst, but it's awkward enough for me to second guess buying 2 of them.