I love my FitBits
Is it 100% accurate? No. Does it need to be? No. It isn't tracking data for scientific research, it's tracking data to give you an idea about how you are doing. And it's great for that.
I have the Charge HR and the Alta right now. The Charge HR had some problems. The back of mine came off a few months after purchase and FitBit replaced the whole device for me. Six months later and the back came off that one, too. Aside from that problem, the device worked well.
The Alta and the FitBit Charge solved that problem by making the whole FitBit piece out of metal instead of plastic. To advance the screen on the Alta to show different data, you tap it. But you have to tap it hard and just right to make it work, which was a problem. The Charge 2 has a button on the side, eliminating the tap it problem. The Alta band didn't have a real buckle and would sometimes fall off. (I bought a buckle band from a third party vendor on Amazon and love it.) But the Alta did allow you to change the band. The Charge HR had a buckle, but it had ONE band for all eternity and you couldn't change the color. The Charge 2 has a band with a buckle and you can change bands and colors. The Charge 2 took all the best features of the Charge HR and the Alta and put them into one device.
I have my Alta set to notify me of calls, texts, and calendar appointments, which is very handy. I also use the Move reminders to get more steps in throughout the day.
I missed the heart rate monitor of the Charge HR on my Alta and it's good to have both. If you want a lot of bands in different colors or materials, you can get them from Amazon. They're much cheaper than the bands sold at FitBit and the ones I bought for my Alta are identical to the ones I got with my FitBit, they just don't have the FitBit stamp.