i have 2 OKO's and am very happy with them so far (i've only had them under one month). i have an 8 MOA on my 9mm AR and a 4 MOA on my new lightweight .223 upper. the 11 brightness settings make it usable in any lighting conditions (in the Arizona sun this afternoon i only had it on #6!).
fast to acquire your target and easy to get back on target when rapid firing. as a bonus, i put the 4 MOA on my new upper on thursday, and when i went to sight it in, it was already zeroed! how often does that happen!?! (actually about an inch high but hey....)
Cavalry Arms carries an QD mount with a steel cover that i have on one of them...it uses two thumb screws to disconnect.
for the price i don't think the OKO can be beat. i also have an EOTech that i LOVE but i actually like the OKO more than an Aimpoint (its the whole "tube" thing i can't get over...).
personal opinion, of course, but its worth a try!