This does exactly what it's supposed to do. From an open or expanded position of the two sides of the binocs, you simple squeeze/push/press all the way together each side and you have the "memorized" positioning between your eyeballs. I'm deducting one star for two reasons ... 1) it really seems like there should be one or two more threads that screw down into the tripod adapter location where this inserts (at least on the Vortex Diamondback 10x42's where I installed it) to make it more secure; and 2) it positions itself against one side (the right barrel, if I recall) and won't stay centered midway between the two barrels once you've moved them a couple times. (This has no effect on its function, however.) If you have large fingers it will take some patience to start the threading but this would be true of a tripod mount as well. I purchased this item because I was afraid of pinching my fingertips at the top of the hinge at some point in time when repeatedly adjusting the barrels to match the correct interpupillary distance between use, travel, bumping, and loaning to others. I used my new binocs dozens of times each day on a recent 10 day birding trip in AZ and never had any problem with this device.
Pros: Effective, unobtrusive, timesaver
Cons: Occupies tripod mount, needs 1-2 more threads
This review was written in the old system and had content requirements that are different than reviews written today.