I had one for a short bit. I believe it was a 1st gen that I bought used. I had come from using an ACOG and wanted something that had a 1x capability as well as a quick "zoom in" function in one housing unit (ie: no magnifier behind a RDS). This seemed to fit my bill as it wasn't as long as a standard 1x-6x optic.
Pros for me:
-Personally, I never had a zeroing issue (only about 500 rounds fired), but even a broken watch is right twice a day.
-I truly liked the features of the magnification lever bar. No twisting a dial. Just flip it over.
-The brightness setting was interesting as it had illuminated red dot options OR illuminated crosshairs on my model (not sure on others).
Cons:
-It's heavy as hell on a carbine
-Bulky! This also kind of fits under the weight as well since it doesn't let you forget it is there.
-Eye relief, as stated above kind of sucks, but I got used to it pretty quick on the carbine. When I used one of the non adjustable magnification ones (M145) on my m240 in Afghanistan, I took it off and never went back due to eye relief. Just food for thought.
-COST!!! I got mine used for $700. that is the ONLY reason I was willing to try it out. Is a brand new one worth the price? No. There are a ton of better options out there IMHO.
If you have any specific questions on it, let me know. I will try to be as fair as I can about the optic, but my recommendation is to avoid it if there are other options you are looking at.