Hi Steven, yes you lose the rear sight when adding an optic.
The most impressive thing about this gun is the trigger. Historically, 1911 triggers are pretty darn good, but this trigger is better than most. The reset is almost nothing. If it weren’t for the nice audible reset, you wouldn’t even know it moved.The pistol’s trigger pull averages around 2 pounds, 7 ounces.
Stay safe & have a great day!

Hi Steven and welcome. Yes, the majority of Optics will have the rear sight built into the Red Dot since the rear sight is a part of the cover plate. The trigger is actually decent on this model. Cheers and stay safe! -- https://eaacorp.com/product/girsan-witness2311-double-stack/