The main things I use the Flex for are the step and distance counts. I like to see how far I'm going during the day. I'd say these counts are fairly accurate - the step tracker takes into account the motion of your wrist, so if you're not moving your arm a lot when you walk, your step count may be somewhat lower. But I've never felt that it's so wildly off to make it a big deal. What it can't monitor is activities where you're not moving your arm - riding a bike is a major one that comes to mind. However, you can add activities using the Fitbit app or website, and by telling it how long you did the activity for, it will add an appropriate number of calories to your daily total.
The tracker has a good battery life. I can usually go about 6 days between charges, and charging takes no more than a couple hours. The bands that you wear on your wrist don't last forever, though. My husband has gone through several already. You can order more through Fitbit, or you can find comparable ones for cheaper on Amazon. They even have cute patterns, like these that my sister found:
|i-smile replacement bands on Amazon|
There's also a social media aspect to the Flex. You can become friends with other people who use the Flex and see how far they're walking each day. I admit, sometimes it's a little disconcerting to see others leaving me in the dust, but most of the time it's fun. You can also participate in challenges through the app: daily step challenges, workweek step challenges, and weekend step challenges. I've done the weekend step challenge a couple times with my sister, and it's funny to see how competitive we get. But hey, as long as we're moving and getting exercise, that's all that matters!
For me, the biggest plus to the Fitbit Flex is how it gets me moving. When I first started using it, I was kind of shocked at how little I walk around during the day. I work at a small law firm, so it's hard to get exercise during the day. Now, I try to get up more often and take a stroll around the office. It's been a great motivator for me.
There are fancier and more high-tech fitness bands out there, but for someone looking for a basic fitness monitor, the Fitbit Flex is a great option!