I've been using the Trijicon ACOG for years as the primary optic on my field rifle. I've seen these things dropped, kicked, knocked into door frames, and submerged in really muddy water and they always do their job. Whether you're in clear daylight with the afghan sun on your face or on a dark street at 3am on patrol, you can see clearly enough to get a head shot at over 600m easy. I prefer these over red dots because you don't need batteries to rely on, and these hold a zero perfect (unlike my old EOTech 551). The only gripe I have or ever hear from anyone else is that the front sight post on our ARs create a blurry dark spot at the bottom of your view. It's not that bad though. And for the OCD people you could always use a riser mount or get a flip up front sight.
I plan on using mine for a long time, and the other guys agree, it's well worth the price.
John the PMC from