I'm interested in the OKO sight for my M16.  I've trashed a Holosight with fullauto fire, but it was a neat sight until it died.  It really had no parallax issues.  I've heard reflex type sights have parallax issues and you must keep your head directly behind the screen for it to be even remotely accurate.

Is the OKO durable?  What would you rate it against in the market place?  Is it quality?  

I'm leaning towards purchasing one, but having never used one or seen one in person I'm reluctant to take that leap of faith.

I like mine. I have used it on  my flat-top AR & on a Mech-tech carbine conversion .460 rowland. No problems. Zero malfunctions. No paralax troubles. In short, I like them very much. They are very easy to mount & to zero. I'll be getting at least 1 more.