For my style of shooting I changes the AE/AF-L button to AF-On, the DOF preview button to My Menu with the top slot set as Auto ISO on/off and the Fn button is now the AE-L function. AE-L is very useful and I need both AF-On and AE-L so this arrangement actually be more effective than on my D800 which has separate buttons next to each other on the back of the camera. By using thumb for the AF-on and index finger in the natural grip position for pressing the Fn(now AE-L) requires less feeling for the difference between buttons as on the closely set buttons on the D800. Using AE-L is essential for control of metering when recomposing or many other scene types. Having both needed buttons so handy when set up this way, I wonder why is it not default and use another button location for Fn.