I have an Aimpoint on one of my ARs that is just like the one the GIs are using. It provides numerous advantages over iron sights. First of all it is much faster to aquire the dot than it is to aquire the sights. Along the same line, you don't have to align the sights, the sight is on the same plane as the target (or so it appears to your eye). Second, you can easily see the dot at night when you can't see iron sights at all. Third you can use the dot sight with night vision equipment if the dot sight is so equipped, which theirs are.
I recently attended the carbine class at Gunsite and had the value of the dot sight proven to me. Within the first couple days, the people shooting iron sights were telling each other that there was no way they could shoot with the speed that the dot sight users could. During the night shoot, they couldn't see their sights at all, while I was hitting the steel every time at 100 yards. Finally, I had no trouble at all hitting pepper poppers at 400 yards. I didn't find the dot to be too large to allow precise enough shooting to hit targets the size of a human torso out to the effective range of the rifle.
I think you would also agree that the sight has proven itself to be rugged and reliable under actual combat conditions. Another frequently mentioned topic is battery life with people saying that they don't want to depend on an electronic device. The battery life is 10,000 hours on the lowest setting and 1000 hours on the highest (brightest) setting. In addition I have the double battery module that has a spare battery mounted on the sight that would take me less than a second to change. Then if I have the sight turned on for several years at a time and those two batteries go dead, I have a spare battery compartment on my GG&G cantilever mount. If all that fails, I can use the iron sights without removing the electronic sight although the electronic sight can be removed in seconds. In addition, you could just use the sight tube as a giant ghost ring which is adequate for short range encounters.
Training is less of an issue because the electronic sight is easier to use and provides faster first shot hits.