I mount a 511 to both of my shotguns. one is a Remington 870 and the other is my Benelli S90. the fast action reticle is superb for close in work so with the range of the shotgun, it is probably the best choice like Grant said.
As far as how tall is the aperture, the EOTech reticle will sit a bit higher then like said an Aimpoint on a low mount, but the cheek weld is not that much taller. It actually gives you a good heads up shooting stance that is more conducive to CQB.