You know I thought the same thing at first. All I have ever used was the 3 dot sight system, and this new two dot thing seemed weird. After just a few mags at the range. I quickly figured the sights out, and found that it was actually faster and a little easier than the traditional 3 dots.
However the Trijicon sights are very nice, and don't have that learning curve... I had a friend buy a brand new XD-9 service model when I got mine. He got the Trijicon night sights on his.
Here is some info from Heine's website explaining how they work:
Heinie Straight Eight Sights
It is a proven fact that the human eye can correct vertical alignment quicker then horizontal alignment.
The Straight Eight Night Sight Configuration consists of a tritium dot in the front and a slightly smaller tritium dot in the rear which glow in the dark (night sights). When aligning this sight picture, put one dot on top of the other dot making an elongated figure eight. Thus, the "Straight Eight". The tritium dots are green in color and have a ten year warranty.
In a stressful sitiuation, you don't have time to worry about your sighting system!
