Believe this is the same (or design) that Carlock talks about in his video. No moving parts, small, light, low profile, cheap and very little to 'go wrong'. From behind the scope, I can still see it just fine.
I use them for all my longrange shooting. I use the one that Sinclair International sells. I prefer the offcenter one, as it is easy to see with my non dominate eye, and then let my dominate eye take back over to focus on the reticle to take the shot. Not a very good pic, but here is what I see with my left eye, while still keeping good cheek weld on the stock, staying in shooting position. I have a couple of the Defensive Edge style to be used with Nightforce rings, but have yet to try them, as I am used to my present method. Will try them after hunting season..