If you have one of the 30 or so first batch NDS uppers with the undersized scope channel cut on the carry handle you now have an optics option.
I bought one of the Primary Arms 2.5x prism scopes w/etched reticle because I have astigmatism and I'm having trouble getting decent groups with my red dots.
This older model has the benefit of a dual use mounting interface, meaning it will go on a flat top or a carry handle unlike the gen 2 stuff.
The carry handle portion is .485" -ish wide and gives a nice tight fit with the "blem" uppers I have on 2 of my rifles.
The thumb screw doesn't come with it so you have to order it separately. (or you can use the screw from the base with an allen wrench)
It's not much bigger than a Colt scope and has better glass, clarity, and field of view.
https://www.primaryarms.com/primary-arms-2-5x-compact-ar15-scope-with-patented-cqb-acss-reticle-pac2-5x
Not my pic.