Mine has been mounted on my A2 upper. The only issue I've had is that you have to be sure to retighten occasionally. I've got about 400 rounds with my scope mounted on 5 separate range sessions. The zero has held! No doubt I've been gentle regarding tightening that screw so as not to strip out the sight base. I recall someone mentioning putting in a helicoil when theirs stripped.
Where I really noticed the benefit was with the Air Force .22lr adapter installed. I can hit large laundry detergent jugs with regularity at 300 yards. At that distance I am holding at the thick base of the reticle. 100 yards is 1.5 dots and 200 yards is 3.5 dots.
I've written a program to utilize the mildot ranging capability. But, without a laser range finder to confirm I just don't know for sure. Based on my testing I believe it's within 15 yards. I've run the program on both my laptop and my PocketPC without any problem, I just need the laser ranging confirmation. Based on the formula supplied with the scope and data on M193, Q3131A, M855, 68gr OTM, 75gr OTM and 77gr OTM I also calculate the number of scope clicks at the calculated range. Required inputs are size of target in inches and measured mils. Results other than scope clicks, are Yards and Meters to target. Based on 16" barrel, 50 yard zero and the above loads.
For such a cheap optic the glass is suprisingly clear and so far it's held up for me and had a repeatable zero. Absolutely worth the money, all $40 + shipping.