10 out of 10 points and recommended
The lens is amazing. Ultra, ultra sharp. Fantastic autofocus, extremely well done. A really professional lens.reviewed June 9th, 2019 (purchased for $2,400)
About the A/m button, you can notice the difference between the M/a button, making this test:
Switch the selector on AM and select AF-S mode on your camera; then rotate slowly the focus ring. While you are turning the ring, release the shutter button just to focusing something. You can notice that the camera autofocus will focus properly the subject. Now, do the same thing with the button on M/a position. You will notice that the autofocus will not work and you will able to focus manually as you like.