Unfortunately there is no lower mount for this sight.
It does NOT have night vision brightness settings. The XPS3 and EXPS3 are the night vision models.
Yes it can use rechargeable CR123A battery.
OPMOD stands for optics planet modification, and are specially made EOTech EXPS2 sights for Optics Planet.
Yes, the Sig magnifiers will work with this sight.
No, as each model comes with either the single 1MOA dot or with 2 1MOA dots. There is not a way to toggle between reticles on this optic.
These sights have the L3/EOTech plates below the window and the updated EOtech logo laser engraved onto the side of the housing as pictured.
OPMOD versions are functionally identical to the to the model of EOTech. OPMOD changes are purely aesthetic in the case of EOTech products.
The EXPS2-2OPMOD has a slightly larger window coming in at 1.20" x 0.85" (30 x 23mm) in comparison to the window on the EXPS2-2OPMOD-KIT1 which has a window size of 30.5 x 21.6 mm.
The EXPS3 models of this sight are night vision compatible, with night vision illumination options for use with night vision devices. The EXPS2 and EXPS3 will lower 1/3 co-witness with standard height AR iron sights. You will need the EXPS3 to be able to use the reticle with night vision.