1) the FDEZ-3 does not change the grip angle for me compared to a factory medium.
2) dry firing, I like it as it gives me more real estate for my support hand.
3) I am just back from live firing it. I set up a few drills, drawing to a two inch square, shooting three progressively smaller circles on a Max Michel target, and doing some doubles to assess splitting ability.
On the first two drills, even though the gun felt different with the hump of the -3, I didn't note a measurable difference in my performance. In the doubles, I was measurably faster with the OEM medium installed. In addition, the bottom of the hump started to hurt the base of my palm on my strong hand.
So considering the shooting results and the pain, I am sticking with the factory back strap.