Fitbit Zip is a small clip-on fitness tracker that tracks steps, distance, and calories burned.
The Fitbit platform allows you to manually input a variety of other stats.
Pro Easy to hide under your clothes
The Fitbit Zip fitness tracker is very small, so you can easily wear it somewhere that it will be hidden (belt, pocket, bra strap, etc.). Unlike most trackers which have wrist bands, you don't have to worry about trying to make it blend in with what you're wearing.
Pro Fitbit app lets you track a variety of health-related stats
The app doesn't only display the stats from your device, it also lets you track a variety of different health-related stats by entering them manually. You can log your food for the day, how you slept, activity, weight, and more.
Con Lacking many of the features that fitness trackers often offer
The Fitbit Zip only tracks distance, steps, and calories burned. It's basically a pedometer with a smart tracking platform you can use for manually tracking the rest of your day. It can't tell you stairs climbed or heart rate, and there is no alarm, sleep tracking, or GPS.
Con Issues with the battery not working
The contacts in the device are very sensitive. If you don't place the battery in just right, it will only work for a short period of time before the battery needs to be readjusted or replaced.
Even when following instructions provided by the company, some people report that still can't get it working properly. The battery may end up lasting days instead of the promised 4-6 months.
You can see how to properly change the battery here.