When comparing Fitbit Flex vs Fitbit Versa, the Slant community recommends Fitbit Flex for most people. In the question“What are the best fitness trackers that pair with iPhones?” Fitbit Flex is ranked 12th while Fitbit Versa is ranked 19th. The most important reason people chose Fitbit Flex is:
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.
Specs
Ranked in these QuestionsQuestion Ranking
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 a great blend of design, quality and comfort
Since the Fitbit Versa is light, flat and waterproof, it’s comfortable to wear all the time – while sleeping, showering, working out or in your everyday life. The LCD screen is made of guerilla glass, which ensures scratch protection and durability for active use. The Fitbit Versa has a clear and bright display, making it easily visible both underwater and in direct sunlight.
Even though the watch’s UI is already designed to give users easy access to everything, the three buttons on the watch can be customizable for shortcuts and commands.
The visual design might not suit everyone, and it might seem cheap and childish to some, but customizability and comfort outweigh this con. The app store offers many watch faces, so you can find whichever suits you best.
Pro Tracks a comprehensive amount of health and fitness data
Fitbit Versa offers all-day heart rate tracking, reminders to move, guided breathing sessions, 15+ exercise modes, sleep tracking, female health tracking and subscription-based on-screen workout sessions, all of which is traced and displayed on the Fitbit app. Although the watch does not have built-in GPS tracking, it can easily be connected to your smartphone in a 30 ft range for accurate tracking of speed and distance.
Pro Long-lasting battery life
The battery life of the Fitbit Versa varies between 3 and 6 days depending on use and Wi-Fi and Bluetooth settings. This also means that you usually don’t have to worry about charging your watch at night and you can properly use the “Sleep tracking & stages” feature. Regarding the charging itself, it takes only two hours to get from 0% to a fully charged battery.
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 Setting up music is a hassle
The watch offers 300+ song internal storage, but transferring songs takes a long while and it's different for everyone. On this forum post a user has said that it took 7 hours to upload ~5.5 hours of music on their Fitbit, but another has reported that it took 9 hours to sync 9 hours of audio. There are many posts on the official Fitbit community forum referring to this problem.
In terms of streaming, the app store only offers Pandora and Deezer as of now.
Con Relatively small app library
Since Fitbit is a relatively new arrival in the smartwatch scene and has a smaller community, its app store offers only a fraction of what other competitors can provide in the third-party app and integration field.
The app store itself is not perfect – some apps and watch faces offer trial versions and need payment for full-time use, which is not always disclosed at first.
