Fidgeting is not a new word, but it recently became popular after a Kickstarter campaign that showcased a cube with some buttons just to avoid distraction during work or concentration. It's here in this link: https://www.kickstarter.com/projects/antsylabs/fidget-cube-a-vinyl-desk-toy
(This campaign was supposed to raise a mere $15,000, instead it grabs the curiosity of over 150K backers and raised a total of $6,465,690. Just think how many people are really in need of the stress reliever or concentrating device!
Many people play with their fingers while concentrating, many people even bite their fingernails. Just to suppress this nervousness many people play with pen holding in hand and doing that "tik tak" thing. It's just in the human nature.
However, a research (a science book) named as "Spark: The Revolutionary New Science of Exercise and the Brain" said that any small repetitive activities such as fidgeting, chewing a gum, tik taaking pens or nail biting, can increase the levels of neurotransmitters in the brain and that would increase the ability to focus and concentration temporarily. In that case, using a fidget spinner (it could be a toy or a DIY spinner) can help you concentrate on your work.
Sydney Zentall, Ph.D., of Purdue University, studied the factors that help children with ADHD succeed in the classroom. She calls these sensory-motor activities “distractions.” We call them fidgets — mindless activities you can do while working on a primary task. We’re not talking about wriggling in your seat. Fidgeting is more intentional. Read here: https://www.additudemag.com/focus-factors/
Other than using the fidget spinners, you could workaround with these methods:
1: walk and talk
2: multi-colored pen and pencils or scented markers
3: listening to music in a mp3 player
4: chewing gum
5: busying the hands by playing with pens, beaded bracelets, toys, paper clips, etc..
6: standing up and moving around
7: setting a timer on your phone or clock and achieve the target
many more kinds of activities to increase the concentration
However, in 2017, the marketing of fidget spinners has moved to the next level and every fidget spinner selling page has started labelling the device as stress reliever fidget spinner, fidget toy to increase concentration, focus and attention. You get it what they want to sell when you believe that it will work.
You will use it for a while and later you won't because it wouldn't work for your concentration. It's just your mind and your way of increasing concentration. You would not need any toys or spinners to increase your focus on your works!
I hope this answer will help you.