My local Memorial weekend festival had fidget spinners for sale, ranging from $12 to over $20, advertised to help with ADHD, anxiety and more. It left me wondering what we know about their effectiveness. It turns out very little. On my go-to research source, pubmed, I could find no single study on fidget spinners or their kin (cubes, etc.). But NPR published two articles exactly two years apart, one on fidget spinners and one on fidgeting. 
On May 14, 2017, NPR published an article on fidget spinners.
Essentially, the article quotes a Duke professor suggesting to stick with what’s known to work.
The professor points out that there’s no evidence that fidget spinners work. Though it’s said, what seems perhaps buried or likely to be easily overlooked is that the reason there’s no evidence is that there’s actually no trustworthy research on them. See here.
Meanwhile, two years earlier, on May 14, 2015, NPR published an article describing a small study that shows that children with ADHD performed better on tasks requiring concentration when they fidgeted. (The children worked while on a swivel chair that they, of course, spun and moved.)
Overall, more movement meant better performance for these kids (kids without ADHD, on the other hand, did worse with movement). The lead author, however, cautioned against both too little and too much movement. See here.
Perhaps fidget spinners would fall into too much movement or the wrong kind (attracting eyes as well as fingers), but it’d be interesting to see some real research on them.
Tonya Lippert 