When comparing Fitbit Flex vs Sensoria Fitness Socks, the Slant community recommends Sensoria Fitness Socks for most people. In the question“What are the best fitness trackers that pair with iPhones?” Sensoria Fitness Socks is ranked 10th while Fitbit Flex is ranked 12th. The most important reason people chose Sensoria Fitness Socks is:
Sensoria fitness tracker gathers information on how a runner puts pressure on their foot and analyzes it in real-time. If the sock notices something that could potentially cause injuries, it warns the runner with a voice message and suggests a way to improve his technique.
Specs
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Pros

Pro Replaceable wristband with lots of style options available
The fitness tracker itself is a separate part from the wristband that can be taken out and put in a different band. There is 10 wristband colors to choose from in the official store, and custom bands available from third-party vendors.

Pro Comprehensive reports of your daily activities
The fitness tracker offers stats such as distance traveled, steps taken, calories burned, weight changes, calories consumed from foods and drinks, restless and awake states of sleep, etc.
Pro Integrates with over 40 apps so you can get the info that's most important to you
The fitness tracker can be integrated with a variety of apps that together can offer more in-depth and complete overview of your health and fitness patterns.
Pro Visually displays your daily progress using LED lights
There are 5 LED lights that, after double-tapping the wristband, display progress towards a goal. Each light indicates 20% progress towards the goal and the tracker allows choosing between steps, calories or distance to display this way.

Pro Tracks weight goals
Fitbit Flex lets users create a meal plan and log their progress from the dashboard menu.
Pro 5-7 day battery
Fitbit Flex will last up to a week on a single charge.
Pro Real-time Bluetooth syncing
Flex constantly shares data over Bluetooth, meaning that the device doesn't need to be taken off in order for the data to sync to an iOS or Android device.
Pro Social layer can increase motivation
Information regarding goals and progress can be shared with friends, and users can even challenge each other with goals.

Pro Quick food and drink logging
Because of Fitbit's database of foods' nutritional information, food and drink logging is easy.
Pro Comfortable
The lightweight rubber band is very comfortable to wear.
Pro Provides feedback on running technique through voice messages
Sensoria fitness tracker gathers information on how a runner puts pressure on their foot and analyzes it in real-time. If the sock notices something that could potentially cause injuries, it warns the runner with a voice message and suggests a way to improve his technique.
Pro Motivational audio cues
A virtual coach can be set up to congratulate when personal records get beaten, cheer when doing well, and warn when not doing as well as hoped. The frequency of audio cues can be adjusted.
Pro Allows adjusting settings to preferred running style
There are multiple valid ways of running. To accommodate runners of different styles, Sensoria fitness tracker allows setting up desired landing positions and cadence as well as turn on a metronome to help out with execution.

Pro Easy access to data
Sensoria provides companion apps for iOS, Android and Windows phones, as well as a web dashboard.

Pro Socks can be washed
Though the fitness tracker is not fully waterproof, the pressure sensitive electronic textile used in the socks can safely be washed and machine dried.
Cons

Con Oversensitive pedometer overestimates your step count
The fitness tracker's step counter often counts movement unrelated to walking or running as steps. It ends up reporting more movement than has actually happened.
Con Hard to get the tapping right to active LED display
The double tap to activate the LED display lights must be the appropriate pressure and timing in order for it to work correctly. This can be frustrating to some users.

Con Unreliable altimeter
The socks sometimes have trouble detecting changes in elevation.

Con Only one sock is active at a time
The socks feed data to a single anklet, and information for both feet can't be gathered at the same time yet. This functionality is planned.

Con Doesn't catch some bad running techniques
Currently the fitness tracker covers a relatively small subset of bad running techniques. It's possible to be in a situation where the technique is bad and the device is not aware of it.
Con Very few customization options currently available
Some of the fitness tracker's customization options are planned, but not yet available.
