Review of the FitBit Flex

The FitBit Flex is now out in the UK and I’ve been using it for a couple of weeks to try it out. The device boasts a new wrist-worn form factor and benefits from wireless syncing and the strongest ecosystem and community of users in the UK for a device of its type. But just how good is the Flex? Let’s find out…

What is tracked?

Just like previous FitBit devices, the Flex mainly tracks steps and sleep. The number of steps is then turned into a distance, which you are shown daily, you can even see how many ‘very active’ minutes you have made, which is essentially your workout (or that rush to work!)

Through this data the Flex will calculate how many calories you have burned, although the figure is not split into resting / active calories burned, so can be confusing to start with and can be difficult to calculate how active you have been.

You can enter your weight manually to track this, or of course use the FitBit Aria WiFi Scales which hook up perfectly to the FitBit ecosystem as you would expect. These are very similar to Withings Scales and are a similar cost.

In terms of sleep the Flex will let you know how much was restless and awake, leaving the rest as calm deep sleep. If you forget to tell your Flex that you’re going to sleep (easy to do if you fall asleep on the sofa a lot like I do) then not to worry, as the Flex can retrieve the sleep data if you just tell it when you wen to sleep and when you woke up. This is a great feature and one that is missing on the Jawbone UP.

Through the app you can track other activities such as cycling that the device would not be able to track itself, this is however manual and the Flex does not feature a timer like on the UP where you can do this quickly through the device. This I missed, however the app is simple to use so it is not a big issue. You can also use the app to track food – or use a third party such as MyFitnessPal which offers a better UK listing of food items.


While I did not use the FitBit Flex at the same time as the Jawbone UP, the data did seem to be of a similar pattern, showing the data is accurate. The sleep data also felt right, there is little way of knowing how accurate that is without a lab – but it felt right and matched how I felt in the morning. Again, just like the Jawbone UP.

I particularly like the way the app represents the data and the graphs that are produced. Through the app you can see steps, calories, distance and ‘very active’ minutes as a bar chart, colour coded for intensity. This snapshot makes the data easy to understand and helps you get a feel of the times in your day where you have the opportunity for more activity or to snack less.


The native app for the Flex is exactly the same one you use for the Ultra, One or Zip. And just like the FitBit One, your Flex can wirelessly sync with the app through Bluetooth. This is a great feature, and one that is missing on the Jawbone UP, that allows you to get instant data reports on your phone with no need to plug in or be near your PC. In fact, the Flex never needs to be manually synced, since a small USB receiver picks up data wirelessly from your Flex when you are close too.

Other apps work with the FitBit Flex too, the full list can be found on FitBit’s app gallery, however one noticeable omission is – a firm favourite of mine which really is a selling point for the Jawbone UP, which does play nicely with the service. For a lot of people this will not matter, however for those of us who want to hack our data and what we do with it, creating fun and useful recipes with, then it could be a deciding factor.

User experience

The Flex is really a fantastic user experience. It fits comfortably on any wrist size, coming with a S/M and M/L attachment band, which both have varying sizes, just like a watch. The actual tracker is a tiny device that slots into the band and can be taken out to get charged up.

Battery life is short however, and at around 5 days on average, it doesn’t even last a week. This is a downside as the more often you have the device charging the less data you’re tracking (it also increases the chance of forgetting to put the tracker back on).

The main thing is that the Flex is wrist worn. With previous FitBits there was the chance your Ultra, One or Zip would fall off whilst out, or still be attached to your clothes when you did a wash. This is no longer the case and it means you can wear it 24/7 – even in the shower and no more waste-of-time sleeping band attachments. On sleep – there is an alarm feature where the Flex vibrates to wake you, silently so only you are awoken. Great, but it doesn’t choose a light sleep period and goes off at the exact time you set.

The Flex is controlled through taps, these are really simple to learn and with 5 tiny lights giving you visual feedback to confirm your commands. I prefer this to the vibration feedback of the Jawbone UP, as the 5 lights can vary more than a vibration and confirm the exact command you intended. It can also represent how many steps you have made during the day without looking at your phone.

The phone app itself is great, the charts are useful and the fact it syncs wirelessly through Bluetooth is good. However, I soon turned the sync feature off – leaving Bluetooth on, on my iPhone, really sucks the battery. And while the app is good, the visuals of the Jawbone UP app – which is sort of like an infographic throughout – is so much nicer. But, unlike the UP, the FitBit boasts an online dashboard too which is far superior and has a well established online community, complete with groups and leader boards.


The Flex is pretty inexpensive at £80 and is well worth buying for anyone who wants to start tracking. However, if you ever want to export your data, you’ll then come up against a cost of £40 a year for the privilege. It seems a little steep and takes the cost beyond the price of other devices, including the Jawbone UP (£100) which allows you to download data for free.


The FitBit Flex is a great device and is the best tracker from FitBit ever. As a wrist worn device, the user experience issues are long gone and you can truly wear the device 24/7 – something that really matters if you want to track data in the long run.

The Flex has its issues though; it does not work with, it has a premium cost to download your data and it has a short battery life. To hackers and data geeks I think this will be an issue and makes a good case for the Jawbone UP being a superior device (which also has twice the battery life). However, there are then some amazing features that the UP doesn’t touch upon – wireless syncing on both your PC and phone, a better display and feedback system and a larger UK community of users.

I recommend the Flex, but suggest you think about what you want from a device. I’m not keen on the fact that you have to pay for your data and would prefer it played nicely with more apps, such as If you’re the same, then opt for the Jawbone UP. But if that really doesn’t matter to you, then get yourself a FitBit Flex.


The Breakdown

User experience
Battery life

There are 6 comments

Add yours
  1. Tomhlord

    Very nice review David. My brother was recently weighing up the Flex and the UP. He plumped for the Flex based upon price and is very happy with his purchase!

  2. Eric Jain

    Nice review! Fitbit requiring a paid account for data export is shameful, but at least their API is open; I’m still waiting for Jawbone to grant me access to their API… Also, any review should include a look at companies’ privacy policies!

  3. jim

    the fitbit flex is a nice item however they need to do something about the band. mine split after just 4 weeks. it’s coming apart at the led bar where it seems to have been glued to the led plastic bar. They probably need to make the strap as one piece instead of 2 and glueing it together. Otherwise it is a good unit. The wifi scales are also really good. Updating your weight to your account. Very happy with the scales. They are excellent quality.

Post a new comment