I'm great at magic eyes / stereograms and have a ton of posters around my house with them, but I still had trouble with seeing the differences in the test images. I easily locked in my focus on the overlapping cat images but only one difference stood out to me. I eventually got them all but it wasn't that easy (maybe with practice I could get there). The differences are noticeable when I focus right on it, but when I'm looking at the whole image it's harder to tell what is missing from one eye.
Are you able to look around while keeping your "unified vision"?
To me, all the differences appeared to be flashing (probably my brain alternates between the pair of images it attempts to "lock in", or something to that effect).
