I've owned the Trijicon ACOG TA01 NSN with a JPoint dot sight on top, an Elcan C79 and the Specter Dr. (The real ones)
There are pros and con for each.
For the ACOG with a dot sight on top. It is the lightest of the 3. Having the dot sight allows you a quick sight for close range and the scope for long range. The only thing is that when you move from the dot sight to the scope, you have to take your eye off the target for a split second and your eye takes a moment to refocus when it hits the scope. But if you take the time to sight the the dot sight to the same point that the scope is zeroed in on. You can move from one to the other relatively quickly,
The biggest drawback with the ACOG is that it is difficult to sight is for 50 yard for airsoft use. I was always having to use the 300 yard range marker as target point. Also, if you turn the elevation dial all the way down or up it can slip of the elevation screw and then it won't move up or down. I had this happen but fortunately Trijicon fixed it for free since no parts needed to be replace.
The other thing I didn't like was that I thought the eye relief was too close. Even if you had your scope mounted all the way to the rear. It always seemed that I had to stretch my neck forward to get a good view.
For the C79, it's weight is in between the other 2. The best thing I liked about it is that the adjustments for the sights are on the mount and not on the scope and I feel is much easier adjust your sights. You can also zero in at 50 yards for airsoft use.
The con in this scope was that there's now way to use any type of sights for close range. The scope is fixed at a X4 zoom. Also the rubber pad around it is big so if you're prone you really have to lift your head to see over it.
For the Specter Dr, it's coolest feature is being able to go from x1 to x4 magnification and back with just a flip of the switch and without ever having to take your eye off the target. Which is very nice. The only drawback to this feature is that you have to take one hand off the gun to do this unless you have some long thumbs (I can do it mounted on an M4)
Also, both Elcans have a much better eye relief than the ACOG.
The other nice feature is that it has 5 dot setting from night to day and 4 illuminated night setting for the crosshairs. So you can use it as a dot sight for quick target acquisition or switch to scope mode. However, in the dot sight mode it's not quite as quick to zero in on a target compared to having a mini dot sight mounted on an ACOG. Oddly enough though. You can mount a mini dot sight on top of the Specter Dr. (See Picture below) The cool thing about it is that you can move the iron sight to the side (Left or right) So, you can have a dot sight inside, a dot sight on top and iron sights on the side. I think there are no optics on the market that has so many sighting option in one unit.
The last thing I like about it are the reticles. Those little circles below work just as well for airsoft too at extreme long range. (See pic below)
The biggest drawback with the Specter Dr. is the weight. It's more than twice the weight of an ACOG.
As for my preference, I sold my ACOG & C79 for the Specter Dr.
A couple of side notes. If you want an ACOG, get the airsoft one because you'll be able to zero in at 50 yards. Of course the clarity of any airsoft scope won't be as good as the real one.
And if you want a real Specter Dr. in dark earth. Dream on. For now, they are for military only.
