Fitbit versa watch is worn by most people 
I actually don't know what a Fitbit is. Is that a new smartwatch?
Fitbit is a new smartwatch with additional features
Do Fitbits keep track of the calories I've burned?
It does and is always advisable to wear it during excise 
Do you know if any fitbits have the capability of sleep tracking?
Am not sure, but some companies are doing that
What is your favorite feature of Fitbits?
Heart beat counts has been my great experience
Do you know where I could shop for a Fitbit Alta HR?