I have one of these and I don't like it.
I have found that the dot is too fuzzy.
I have found a slight parallax issue, where point of aim is slightly affected when your cheek weld changes.
If rain gets on it just right, the light will scatter. My friend had this happen at our shooting match. He couldn't see the dot.
The lens/reflector works by filtering colors so that the red light will reflect off of the back and to your eye. This color filtering effect, for me at least, made certain targets hard to see in certain lighting conditions. When the paint had worn off of the steel plates a little, and it was muddy out, there was less distinction between the plates and the dirt.
My buddy eventually broke his OKO after trying to tighten the *plastic* mounts it has.
This sight was OK or me for a while. I eventually upgraded to a Leupold CQ/T. I really like it.
You get what you pay for.