Erin Silver of the Washington Post has written a good article on the subject of fidget gadgets in the classroom.
In my experience, especially working one-on-one with students, fidget gadgets are a distraction. Instead, I work with students to help develop the skill of keeping focused for a period of time. When the student starts to have difficulty keeping focused, even when they are trying, it is time to take a small break where they can fidget, look at their phone, stare out the window, do jumping jacks or walk around the room.
Another strategy that works for me is to change what the student is working on... If we have been working on Algebra, switch to Art.