The latest activity tracker from Fitbit, the Flex ($99.95, direct)($62.99 at Amazon), is a design departure from the signature clip-on style devices that made the Fitbit name. The superb Fitbit One($329.95 at Amazon), released last year, easily earned our Editors' Choice, as did its predecessor, the now discontinued Fitbit Ultra. With the increasing popularity of bracelet-style fitness gadgets, however, it seems only fitting that Fitbit add a band to its collection, and the Flex certainly holds its own in this category.

The Flex is $30 less expensive than the Jawbone UP($28.49 at Walmart) and $50 less than the Nike+ FuelBand($204.00 at Amazon), the two most popular wristband fitness trackers. Remarkably, considering the low price, I like the Flex better than both. Dollar-for-dollar, I'd rather have the Fitbit One, though, because it's a much more versatile piece of hardware: You have more options for where to wear it (pocket, bra, belt, etc.) and the device's display tells the time, distance covered that day, as well as the number of stairs you've climbed. The Flex has nothing but a few blinking lights that indicate how close you are to reaching your daily goal. The One remains my favorite activity tracker at the moment, but the Flex is your best bet if your heart's stuck on buying a wrist band, in part because you get all the other benefits of Fitbit, namely the website experience, which is among the best I've seen.

Fitbit Flex Basics

Designed to be worn all day and all night long, the Fitbit Flex measures your total activity for every 24-hour period, including how much sleep you get at night. It counts steps and miles traveled per day, calculates the calories you burn, and with the website or mobile app (for iOS and Android) you can also count calories consumed and factor in additional activities, such as biking or swimming, which Flex can't measure on its own. Like the Fitbit One and the Jawbone UP, the Flex has a silent alarm that vibrates to wake you up without disturbing anyone else in the room. The Jawbone UP has a neat vibration feature that lets you set it to shake once an hour if you've been sitting still that whole time. I would love to see this same feature ported over to Fitbit's line of products, and it's the UP's singular best asset.

Unlike the Fitbit One, the Flex does not have an altimeter, which measures flights of stairs climbed and other elevation changes.

One new metric Fitbit added with the Flex is active minutes, or the number of moderate-intensity cardio minutes you have a day (the Center for Disease Control recommends at least 150 each week).

Design

As its name suggests, the Flex is flexible, about as comfortable as the similarly slim Jawbone UP, and much less distracting to wear than the harder Nike+ FuelBand or the terribly clunky Larklife.

The Flex comes in two sizes, small and large. Each slim band wraps around the wrist and fastens with two prongs along a set of openings so that you can adjust the fit. In the box you'll receive a band with a tiny piece of hardware tucked inside, which is the actual tracker, as well as a USB charger, and USB dongle for wireless syncing. To charge the tracker, you pop it out of the band and connect it to the USB cord. And since you can pop it out, that means you can also swap out the wristband for a different color. Fitbit is selling the Flex in black or slate, with three other colors available: teal, tangerine, and navy ($29.95 for all three, or $14.95 each). Theoretically, you could pop it out of the band and tuck it into your pocket, but the results wouldn't be as accurate, according to Fitbit representatives, because the device is specially calibrated to be worn on the wrist.

As mentioned, the Flex doesn't have much of a display. Five small LEDs act as indicators showing 20 percent increments of how close you are to achieving your goal (such as walking 10,000 steps, the default). The band vibrates once you hit your goal, but you can't get any information from the device itself—a huge reason I prefer the Fitbit One.

The Flex scored big bonus points with me when I heard it had Bluetooth and NFC capabilities, meaning I could sync the band wirelessly with an iPhone or Android device anytime I'm on the go and want to see my stats in the Fitbit app. Most of the time, I rely on the wireless syncing enabled by the included dongle. Anytime you're within about 10 feet of your computer, the band syncs. As a result, my stats are frequently refreshed during the work week (I have the dongle on my office computer currently), but I can always update them using Bluetooth on nights and weekends.

Setup and Use

Setting up a Fitbit account and linking it to your Flex takes hardly any time at all. Plugging in the USB base station and connecting the tracker initiates a small download on your Mac or Windows computer, which enables the wireless syncing for your device. You'll see an on-screen prompt to create a Fitbit account or log into an existing one. From there, you'll enter a little bit of information such as height, weight, age, and sex so that Fitbit can calculate how many calories your body burns.

If you want to lose a few pounds or maintain your weight, the Web account can calculate how many calories you should eat in a day—and it expresses it in a range rather than a set number, which I really liked. There's a food logging tab where you can record what you eat, as well as some other tabs for managing the silent wake alarm or entering additional activities not counted by the Flex.

You can also configure the Web account to integrate with big-name calorie-counting apps, such as Lose It! or (my personal favorite) MyFitnessPal.

The Fitbit online account has a ton to offer. Pair your Fitbit Flex with the Wi-Fi enabled bathroom scale Fitbit Aria($107.21 at Amazon), and you can have all your weigh-ins logged automatically. You can even keep tabs on your blood pressure and glucose if you have the right devices. The compatibility with other apps is comprehensive and adds value to an already top-notch device.

The battery of the Flex, and really all Fitbit products, has remarkable staying power. You can easily go days without recharging it (another great feature of the Web site: it estimates how much power you have left). When I spoke with some representatives from Fitbit, they explained that a few of the features not found in the Flex (no display on the device, no altimeter) were conscious decisions designed to keep the band lightweight and comfortable, the price low, and the battery life long. Having spent several days wearing a Flex and forgetting it was there within a few hours of first putting it on, I think they made the right choices.

Flex Your Flex

If you specifically want a wristband activity tracker, the $99 Fitbit Flex is the best you'll find. It's extremely comfortable, very competitively priced, stylish, simple, and most important of all, comes with all the benefits of a Fitbit.com Web account. Because of the way it wirelessly (and effortlessly) syncs to your computer, iPhone, or Android phone, it's also extremely convenient. The sleep tracking and silent wake alarms are wonderful features, although I'd love to see Fitbit steal Jawbone UP's "idle" alarm feature—a shake to remind you to get up and move once an hour.

For my money, the Fitbit One remains the best activity tracker on the market, and our Editors' Choice. But if you'd prefer to wear a tracker around your wrist, don't hesitate to order a Fitbit Flex.

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