The Bering Optics Tactical Rubber Eye Guard is more rugged than the standard rubber eye guard that comes stock with the optic from the factory and also has much more surface area to keep it in place.  This eye guard fits the Hogster Stimulus, Hogster R25/35, the original Super Hogster as well as the new A3 version and Bering D-series Night Vision Optics.  As you can see in the 2nd picture this eye guard fits over the top of the diopter (eye piece) adjustment ring which makes its much harder to fall off or lose while also providing a nice rubber texture for adjusting diopter focus.  In the 3rd picture you can see the overall diameter of the eye guard is larger which when found to be more comfortable in general.

The Tactical Eye Guard is the bottom picture in both the 2nd and 3rd pics.