How are you going to mount it? You have three options - 1) RS regulate off the optic mount if you have one 2) mount a rail to the top cover 3) ultimak or other rail system / replacement gas tube?

RS Regulate makes awesome stuff. That being said I am more of a fan of an Aimpoint on an ultimak. Like the RS it is not a permanent modification.

The mounting of a small pic rail like a stormworks - https://stormwerkz.com/scope-mounts/...k-scope-mount/ allows you to mount an RMR which makes it a very small profile.

Legion also makes a pic top cover - https://www.legionusa.com/top-cover-...u-krinkov.html