I have the Activity Tracker Pro from the same company and their website says it has all the same features as the Tracker II, so I’m guessing the differences are more about form than function.
For a basic activity tracker, it does just fine and the battery life on mine is exceeding the 5-day life they say on the website. Just have to sync it with your phone every day or so to use the app that shows you graphs of your activity, steps, and sleep.
You do have to tell it when you’re going to sleep (sometimes I forget), but it will eventually figure out you’re awake in the morning and automatically switch to active mode.
I like it. I’m sure it’s not perfectly accurate, but it does give me a basic sense of activity level and my quality of sleep, which is all I need.
The only issue I have is I can’t read the clock/step-count in daylight. If I’m inside or it’s night, no problem. To me, a minor issue, but might be a deal-breaker for some.