Some folks like front night sight only (me included) while others like the front and rear tritium inserts. It's primarily a personal preference thing. I have played with with three dots, figure eights and express sights (I do work at XS Sights-you will see this again in a moment-and yes, I am biased towards our products), but I have not played with a bar dot or a box dot configuration rear. Even in the best of circumstances, I find them too busy for my taste.
As to why I do not use a rear night sight: I don't like the extra illumination on the rear. First and foremost, if your rear tritium inserts are not installed correctly, or your front sight insert is a bit older than the inserts in the front, then the rear sight is brighter than the front sight. This is not a good thing. The way that our eyes work, they do not see beyond a light source very well. The brighter the light source, the harder it is to see beyond it. If the front sight is brighter, your eyes will be drawn to it. If the rear sight is brighter, then you will have difficulty seeing the front sight. You can use different colored inserts (such as yellow or orange inserts from Trijicon) to alleviate this. Green is the brightest color tritium available (green is also a color that they human eye picks up very well). This also prevents you from mis aligning the sights.
The second reason I prefer a front night sight only is simplicity. It is visually confusing to me (yes, I am simple minded in case you were wondering) to have both front and rear night sights. I have taken a couple of classes oriented towards defensive shooting in lowlight (SureFire level one trainer/operator course and the Tac Pro Shooting Center Pistol Fight at Night class) using both front and rear tritium and front only tritium sights. I have found that the green glow on the rear sight (even a very dim one) is distracting to me. In the case of our express sights, if there is even a small amount of supplemental light (1/4 moon or more, street lights, LED keychain light, candle, etc.), if I can see the target, then I can see the sights well enough to make hits at 25+ yards. Of course, the white line is very bright by itself and is extremely easy to see.
As I said, it's all a matter of personal preference. If you have a friend that has front and rear night sights, see if you can borrow his/her handgun and look at them. Play with them in good light, twilight and full dark at varying distances. See if you can find out what works for you.
Joe
