I've had a OKO on one of my carbines for 5 years and it's my favorite red dot type optic. The open style is as fast as the Eotech, but with the window mounted on the front of the body, it's even more natural, IMO. It's got a 4 MOA dot like an Aimpoint and is just as clear and bright as a Comp M2. The OKO is also very, very light. The body is polymer, but I use one of the factory steel gaurds/mounts (not unlike the Eotech) and it still weighs less than 5 oz.
This thing has been through two carbine classes, over 12,000 rounds, lots of bangs, bumps and tosses and has never lost zero. The battery life is good as well with over 1500 from a cheap, common coin style battery.
Now I am in need of another dot optic and the OKO has spoiled me. I don't have much desire to spend $500 on an Aimpoint or Eotech that I don't like as much. It's really a shame that the OKO is no longer imported.