Optic Characteristics for an AR-15 Pistol

[stomridertx]

I think I'm picking up on what you want to achieve here, and I think you should treat it just like a RDS for a regular pistol. You cannot have any eye relief restrictions and you need it to be as lightweight as possible. Think RMR, Holosun 407/507/508/509/EPS, Aimpoint Acro, etc. Traditional AR backup iron sights are a no-go with one handed shooting with a brace because they are designed to work with the aperture close to your eyeball. There is no good solution to put notch and post pistol sights on an AR, so it should be an optic-only affair. One handed shooting with the brace as they were originally intended is awkward to begin with so you'll really need to find the sweet spot on the rail for the RDS and it may or may not benefit from a higher mount. You might want to buy a few different mount heights and return or sell the ones you don't use.
I know you said this is not about the coming ATF pistol brace ruling so forgive me if I'm speaking out of turn. If by chance you are looking at passing the worksheet point system, that is out of play now and they are going to flat out say the braces make an AR pistol an SBR. They are proposing "amnesty" to get them registered under the NFA for free. Hopefully lawsuits and November elections will make them stop this nonsense, but that's how it stands right now. Trying to make a build using the points system is going to lead to heartache.

[Casual Friday]

I just buy Aimpoints and move on with life.

Proven durability with a track record measured in decades
Battery life measured in years without using solar panels, auto shutoffs, or motion activation
Manufactured in a country that isn't China

[Nephrology]

I like reflex sights (holosight/red dot) of some kind, but also have an 11.5" SBR with a Razor 1-6 on it. Great gun.