In Shulchan Aruch (Orach Chaim 96) it is stated that one is not allowed to hold any object while davening because it will worry him that it may fall and take away from his kavana.
However one is permitted to hold onto something that is needed for the prayer itself (i.e. a Machzor or a Siddur, Lulav and Esrog) thus it will not take away from his kavana.
Fidget spinners have been marketed as toys that are helpful for the autistic and for children diagnosed with ADD. Supposedly, fidget spinners and fidget cubes are claimed to help with aiding the children's concentration during class. Many schools and teachers allow them in their class for this purpose.
If using a fidget cube/spinner helps one focus on the teffilah, may one hold/spin it while davening?
Are there any other factors beyond concentration that may allow or disallow their usage?