Owned four various Arken optics. Sent two of them in for repair or sold them after they refused to hold zero. I suspect that it is from the constant vibration of our uber-rough "roads" and our quads/Sxs's. I still recommend them for light use and day hunts, especially considering their price point.
My Vortex Viper took a poorly timed crap on me at the Best of the West NRL-H match a couple of weeks ago and the backup rifle I used had an Arken 5-25x on it. Did not have any issues with that one.
My only other complaint about them is their weight. On the other hand, when they do lose zero you can beat a hog or bear to death with your optic. So, there is that.
Glass is good enough (as Form points out - it's an aiming device not an optical scanning device), tracking works nicely and as it should. If I like the Shoot2Hunt optic when I finally get my hands on one, I will likely retire my last couple of Arkens.