I’m on my second version of Fitbit device. I bought my first one in 2013. That one was always clipped to a waistband or pocket, or even on the ankle of my bicycling pants. It was pretty reliable in terms of reading actual walking/running activity, but couldn’t be worn in the water. Fitbit actually replaced the unit once or twice when it bricked and wouldn’t power on anymore.
The last time that happened, my model was no longer supported so I got a new version, and this one I wear on my wrist. It does seem to rely a little bit more on arm movement but still seems pretty accurate nonetheless. Bonus is, I can put it in water lock mode and track swimming. The hilarious thing is that when I do laundry and have a folding session, the Fitbit reads that activity as swimming, LOL!
I am disappointed that it no longer tracks “stairs” and climbing — my hikes vary and some of them are very hilly, and I like seeing how much climbing I’ve done.
I find it useful to see how much activity I’m getting in any given day, even those in which I don’t get in a “real” workout. Activity around the house can rack up 10,000 steps when I’m cleaning or doing other projects. The Fitbit also tells me how many minutes I’ve spent in various heart rate zones, and it tracks my sleep if I wear it at night, which can be enlightening too!