I have been a FitBit user since I ordered an original unit on September 29th, 2009. I had forgotten the unit and it went through the wash and died. I replaced it and continued to enjoy the information it gave on my activity. A few years later the FitBit Ultra was released (it tracked vertical distances traveled) and I upgraded again.
In early 2013, Fitbit release the Fitbit Flex. They were in high demand, so it was June before I was able to acquire one.
The Flex regressed in design as it could no longer detect vertical travel and its display digressed to a 5 dot LED display. The older versions of Fitbit could show numeric info (steps taken, miles walked, calories burned, etc) and the Flex can show percentage of your daily goal in 20% increments (based on the number of LED dots that illuminate when you double-tap it).
Additionally, I can 'rapidly tap' it to let it know I am going to bed so it can start recording my sleep paterns.
The form factor is awesome; it clips on my wrist, it is waterproof and I only need to charge it every 5 to 7 days (I get an email when the battery is low- or the companion iOS/Android app lets me know the battery status).
The 'tapping' input is about to drive me nuts.
I have it set to provide an alarm clock function at 8:00am. At this time, the band will start vibrating until I 'rapidly tap' to acknowledge the alarm. It takes me about a full minute to get the unit to exit alarm mode- and more than often it will go into sleep recording mode which requires more taps to get back to normal.
Last night I attempted to double-tap the unit to get an update on my steps taken. It went into sleep mode and it then took me another 3 minutes to get it to go back to normal- up to the point of taking the band off and beating it against the steering wheel for a good 30 seconds.
This behavior appears to have worsened with age as 3 months ago it was very responsive.
I am considering pulling my old Fitbit Ultra out of storage and giving up on the Flex- it has become just that annoying.