I just want to say, that I have the
Nikon DK-17M round 1.2x magnifier on my D810 and it is well worth the price. I am always worried it will be hard to see the info display at the bottom, but that is not the case with the D810. In addition, I shoot a lot at the 1.2x crop for a little more 'reach' and to boost the frame rate so what the crop taketh away, the magnifier giveth back!
BTW, I liked it so much I popped for the square one for the D7100.
Since this isn't something a lot of people think about, I figured it might be a good 'tip' for some, especially the older crowd like me.
v/r
Dave