Thanks for the useful replies, guys.
I kinda wondered how useful the rear tritium sights would be since a good, consistent cheekweld would go a long way towards having your eye "in the right place", which would indeed be very close to the rear ghost ring. "Nose to the CH" I always say with an AR-pattern rifle.
I also wondered about the difference in aiming points due to the tritium dots being lower than the top of the front sight post. I have no illusions about shooting, and hitting, things in the dark at anywhere near 200yds. I was thinking more like in an urban environment with shot ranges not usually to exceed 75yds or so. Within those parameters I fully believe that tritium night sights are very useable.
To those who say "get a dot", I have but two questions. First, what are your plans when your dot sight fails? And second, what if it fails in the dark?
I have trouble bringing myself to dangle all that addorted stuff off of the front of my gun like so many of the "tactical" types around here like to do. Flashlights, lasers, rails onto which to mount all that stuff, etc. It goes against my nature and better sense to hang all that heavy stuff on the nose of the gun instead of becoming proficient with the weapon in as close to the original design as possible, which is light and trim, since that design is well proven to work. Also, flashlights REALLY give away your position, which is not something I care to do when the SHTF. To that end, I asked about tritium night sights as they would add no weight whatsoever to the gun nor would they give away my position.
If I wanted to carry around a heavy gun I'd grab one of my .308s.
That said, I prefer a dot to a vertical line, and the XS looks like it positions the dot very high up on the post. This should allow one to continue to position the intended target on top of the FSP instead of having to guess how much space to leave between the dot and the target. I only wish it had squared shoulders like a normal FSP.
So, I guess I shall try the the XS "dot" front sight post.
Eric