Those will work on the NXS occular! I have had several of the NXS scopes for quite a few years and have always hated that the entire occular rotates with zoom. Pretty much rules out all the flip versions. I have an old Uncle Mikes cover that I keep rebuilding that is 2 hard rubber caps connected with a heavy rubber band. It also attaches to the scope body so you don't end up losing it in the heat of the moment.
But I like that ISC idea and will be checking them out.
I'm right-eyed and right handed. My scope has focus/parallax on the left.
I mount the caps so the rear one swings left, and paint the inside with white or insert a white card stock inner liner, and then shoot with both eyes open. Another approach is to put a square of transparent but frosted tape over the optical center of the non-aiming eye's lens. Both techniques permit light to enter the non-aiming eye, while denying any discrete object to focus upon.
Do not squint, never squint. It becomes uncomfortable and distracts the shooter.
The eyes work in unison, under involuntary control of the brain, to increase pupil size to admit more light under lower light conditions. This is true under all light conditions, so if the left eye gets less light (as in using a black eye patch, etc.), the right eye pupil widens.
This is no good, because, as photographer can tell, you, a wider pupil delivers reduced resolution. This why I use the white inside on the cap. More light through the one eye results in a smaller pupil on the other, and allows vision with greater resolution in the aiming eye. We are talking a points difference here.
If left eyed, sides are reversed in the above description.
We learned this while on a week long Marine Corps League trip to Quantico, to train under the pistol team's tutelage in around the mid-90's.