In theory it's supposed to alleviate stress, anxiety, etc. I thought about getting something like that to keep my hands busy during the dreadfully boring meetings at work. I think a device like this might help me pay attention better (those fidget cubes would be best) because something else is going on. Like listening to the radio while driving, or having a show on while doing a project.
What I do know is that I try to avoid fads, so I won't be getting something like this any time soon.