Fitbit Flex review

The Flex by Fitbit is a fitness tracker that lets you monitor your steps, distance, calories, and even food intake. It's lightweight, versatile, and can be swapped out for many different colors on the cheap. As trendy as it may be, how good is it at actually making you aware of your activity? That's what we're going to attempt to find out...

Before beginning I'll preface by saying we began our evaluation with the Fitbit Force but after Fitibit discontinued it due to skin irritation issues, we decided to replace it in our comparisons with the Flex. In most respects, this review should cover both. The main differences are that the Force tracks stairs and has a full display. In other aspects they're technically identical products.

My first impression of the Flex was that it was lightweight and comfortable to wear. I don't particular care for the clasp type though. It's easy to snag on clothes, particularly jackets. It also is somewhat awkward to take on and off. Be sure to listen for an audible 'click' when putting it on to make sure it's secured well.

Fitbit Flex review

Moving past the clasp, the actual tracker itself gets past decent battery life due to the low maintenance display. There are only five indicator lights which represent 20% each of what you have already completed for your daily goal. For example, if steps are your main goal and you set your goal as 10,00 per day, the Flex will light up an indicator light for each 2,000 steps you walk. You can change your goal inside the Fitbit app to represent steps, calories, or distance.

The Fitbit app itself is where most of your data lives since it's what the Flex transmits it to. You can then compare data over several days or months as well as track weight and sleep. The sleep logging feature has the ability to track deep sleep and light sleep. There are sensitive sleep modes as well so if you don't want it to track things like rolling over, disable it. The Flex does a decent job of tracking sleep but I didn't find the data to be as accurate when compared to that of the UP24. It definitely isn't a deal breaker though.

Fitbit Flex review

I also haven't been pleased with the way fitness tracker apps handle food tracking. Fortunately there are lots of other apps out there that specialize in it that can pick up the slack. Fitbit isn't alone in this instance though so I don't ding them for it. It would however be nice to see them tie in third party support for apps like My Fitness Pal. This is a feature I really like about the UP24 app.

The Fitbit system doesn't just track active calories but calories you burn just being alive. So don't be surprised if you see that you've racked up calories just sitting. It takes energy to just be alive and that's where those come from. However, I do feel that Fitbit overcompensates for calories and steps. During several workout sessions the Flex and Force both showed far more steps and calories burned than it should have. Other trackers weren't spot on either but they were closer together and more accurate in my experience.

The good

  • Comfortable to wear for extended periods of time
  • Great battery life
  • Interchangeable bands are available in lots of color options
  • Cheaper than many other options
  • Custom alarms let you remind yourself of anything with a gentle vibration on your wrist

The bad

  • Calorie count is exaggerated in my experience, as is step count in some instances
  • Clasp on the band can easily get snagged and come undone

The bottom line

Fitbit Flex review

The Fitbit Flex is one of the most versatile trackers when it comes to style but it isn't the best on the market where accuracy is concerned. Unforunately I had a similar experience with the Force which concerns me and makes me lean towards other offerings instead.


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Allyson Kazmucha

iMore senior editor from 2011 to 2015.

  • Alison, As a happy Fitbit Force user, I am possibly biased, but I have a couple of questions for you.
    When setting up the Fitbit, did you set the dominant/non-dominant arm appropriately (non-dominant is more sensitive)?
    You seem to imply that Fitbit doesn't sync with MyFitnessPal, but it does - I've been using it that way since day one and the combo is great.
    Also, why do you think the calorie count is off? You do realize that it is estimating base rate as well? It seems to agree with MyFitnessPal on that score - since I don't see MyFitnessPal incorporating large adjustments from Fitbit activity unless that activity is significant. Anyway - it works for me since I'm using it as a relative comparison over time - the exact counts don't matter to me - just that I maintain a consistent level of activity without over-eating. And one final question - what kind of workout are you doing that registers 6,000+ steps but only 3 minutes of activity? My morning walk to work will register about 20 minutes for only about 2,000 steps - I walk quickly, but certainly not race-walker fast :). Though I know that I can play competitive badminton for over an hour and only register a few minutes of activity for many steps so I'm curious about what other types of activity might have the same quirks. Sorry they pulled the Force - mine's not going back. I hope they get it back on the market soon - the stairs climbed and the display were the tipping point in my decision to buy. Sent from the iMore App
  • Allyson - sorry about the incorrect spelling of your name in that last comment :( Sent from the iMore App
  • Thanks a ton for these reviews. I am in the market for a fitness tracker and your reviews are making the decision easier. Keep up the great work!
  • 502. That’s an error. The server encountered a temporary error and could not complete your request. Please try again in 30 seconds. That’s all we know.
    Got this when I tried to play the video within the iMore app. It is a Google error. FYI. Great review by the way. Sent from the iMore App
  • I can't comment on the iPhone app since I'm a BlackBerry user and we don't get a FITBIT app that will sync but maybe there are some settings missing in the App. I did my setup the old fashion way and used a PC to goto the website. After doing the initial test of counting off steps over a specified distance I was able to set my stride length for walking and running and it has been accurate ever since when doing exercise (I was testing it regularly when out walking or on the treadmill). Note, there are times when it has been overstated on long car trips or sitting in the office as I do tend to talk with my hands a lot. During an hour and a half car ride when I was driving registered 0 steps but when I was the passenger on the way back it registered just over a hundred. Also the step count validation was done using the Force. I developed a rash and had to switch to the Flex and left my settings the same. I had the Force for a little over 6 weeks and the Flex for around 4 weeks now. When I compare my averages on the Force to the Flex they are basically the same so I'm assuming the Flex is as accurate as the Force. I don't pay as much attention to calories burned but based on my height and weight entered and using online calculators to determine calories burned it seems to overstate resting rates a bit. Also if you go to the website you can link a bunch of apps to your account and flex (Lose It, myfitnesspal, sparkpeople, etc). I alternate between Lose It and the Fitbit default one. It just depends on what device is close by when I go to log my intake. I'll look to pick up whatever they replace the Force with as I really liked having the full display (maybe it would be better if my phone sync'd with the Flex) but in the meantime the Flex is great. Also, one of my favourite things with the Force/Flex is the silent alarm. I find it much better to be woken up by a small vibration than beeping of an alarm clock. Negative part is that it takes a bit longer to change the alarm if you don't want it to go off for some reason. Again that would likely be much easier if I would just switch to an iPhone and got into an ecosystem that supported app development.
  • I've had the Flex since it came out last summer, and I love it. Like blyths above, I have been using it in conjunction with MyFitnessPal since the day I got it. They work quite well together. I did have a failure of the original band, but I've been using one of the replacement bands for more than 6 months with no problems. You mentioned that you found it overestimating your steps. I find that it underestimates mine when I have it on the dominant hand (and set as such in the software) and only slightly overestimates when on the non dominant hand (and set appropriately in the app). Still pretty close either way.
  • I have had the flex since July of 2013 and to get a more accurate step count, I put the band in my back pocket. That way the number doesn't jump up by hand moving around... at my desk moving paper around for example. I really enjoy the sleep monitoring function. You can REALLY see how much sleep you are getting. I average about 7 hours per night.
  • Thanks for the review. Sent from the iMore App