I actually have a fidget spinner, and I use it fairly often to keep myself busy if I'm not really doing much. A side effect of my ADHD is that I need to constantly be doing something with my hands, and fidget spinners actually work really well for that! I don't get distracted by it, it's just something that keeps my hands busy.
That being said, though, it also acts as a harmless distraction when I'm feeling stressed and need to take my mind off things. So it is helpful, I just don't like when people make a big deal out of them and get them just because it's cool to have one. They serve an actual purpose, but kids have turned them into a trend.