I have had the SIII with zero stop for a couple months now. So far it's proving to be a great scope. Clarity is good and the clicks are crisp, not sloppy. I was concerned with durability but after beating the hell out of it attached to my rhino the zero held true. The sight has returned to zero after numerous occasions of shooting out to 800 yards with no concerns.
The zero stop is easy to use and has held tight. It's a collar with set screws that screws up to but against the turret. Much like a reloading die. Simple and easy.
My only complaint is I dislike how the turrets are locked into place by a single screw. It makes zeroing difficult
Overall great scope for the money and I look forward to seeing how it can hold up while I continue to beat it up. I primary use it for Coues Deer hunting in the high desert and that terrain is not forgiving.
I hope this helps someone out.