I had never heard of ZCO until last year when an ELR waffle page I’m in ran one. I talked to a few guys since then, lots of folks rank them above Nightforce ATACR’s, on the plane of Tangent Theta’s and Kahles’. I’ve only looked through one a few times, but it seems that is an apt comparison. There are times when a $1,500 scope can’t see at all through the soup, a $2,500 scope can resolve the edges, and then these $3,500-4,500 scope brands can resolve the entire target through the grossness. Nothing fixes an image warped by mirage, but some of these optics will let you see the swirled image, while others will totally lose it. The difference rarely rears its head for most shooters.
Admittedly, spending more than ATACR money, I’d only buy the Tangent Theta.