Fitbit Charge 3 does what it's supposed to.
I had the Fitbit Charge 2, then the Ionic. The Ionic packed up when water got in and Fitbit wouldn't replace it. I preferred the Charge 2 because it uses GPS from your phone, so doesn't flatten the battery in a couple of hours when using it to monitor a bike ride or very long run.
The battery in the Charge 3 lasts much longer that the Charge 2 (12 days vs 5) and everything else seems to work better. The functions are more or less the same. You can find detailed online reviews that explain the differences.
I use a Fitbit mainly to monitor my heart rate during sport. I recently got incapacitated due to blood clots in my lungs, which is what prompted me to get another Fitbit after my Ionic packed up a year ago. It's really good to be able to see what happens to my heartbeat as I get back to normal health. I can see when I'm pushing too hard.
Some people say that the heartbeat monitoring isn't reliable. All I say is that there is a clear correlation between what it shows and what I'm doing. I think it's more than accurate enough to give you a good idea of what's going on with your heart.
Note that the Charge 4 has a lot of new features, one of which is its own GPS, so loses one of the advantages of the Charge 2 and 3 regarding GPS battery life for long sessions.
Verified purchase: YesCondition: Pre-owned