Red dot on vang comp rail

I have a rem870 with the van comp sight/rail combo. Im curious if anyone on here has a red dot mounted on their rail and if it co-witnesses or not.

Im looking into the vortex sparc 2 as the red dot of choice for me but looking for peoples reviews or opinions.

Co-witness means absolutely NOTHING on a rifle, pistol or shotgun!!! A RDS and/or iron sights on a shotgun are worthless. If you need more aiming precision than beads offer you need to either learn how to shoot a shotgun or use a rifle. The exception may be games in which you have to use a shotgun.