looking to add back up iron sights,

Are most good, or some significantly better?

This particular carbine has a Holosun 510 green dot, and If I'm following this correctly,

I'd like absolute co-witness...flip up. The Holosun is not on any type of add on riser,

Not looking for a peep or ghost ring sight. (I think), but that's what most appear to be.

So, absolute co-witness, flip up, and low enough so when down doesn't interfere with the Holosun.

I prefer these.
[Linked Image from i.imgur.com]

Magpul pro sights. All steel....pricy but good. MI industries makes decent sights in my opinion as well.

No peeps or ghost rings gets rid of all the good options.