The article makes the point that in order to benefit from the AF-ON button you need to commit to learning a new technique that makes the AF-ON button your only autofocus method, as opposed to just using it instead of a halfpress occasionally.
I have just started using it and having some trouble. I am left handed and use my left eye in the viewfinder. This places the rest of my face to the right of the VF, directly over the AF-ON button and not leaving much space for my thumb to activate the button. Feels weird but I will keep trying for a while.