These are popular as ****, and well made as much as cheap burritos.
Problem I see is that they all seem to have 3 things in common:
specific bullet weight used
specific bullet velocity
specific barrel length
So yes, a BDC scope that's "garunteed" to 800 yards would be nice, but what does a fellow do when his rifle wont shoot that particular bullet weight, or shoot it accurately as that specified velocity?