I took delivery of a SIG Romeo4T RDS for the new Rattler, and immediately tried it on the CROM. It has a long nose like the Holosuns - it would require either a notch in the sight housing or a modified hex key. Plus (and since the CROM isn’t mounted this is pure speculation) it may be tall enough to not allow co-witness. Not sure if I’ll order one for the 1301T or not.