I'm going to go against the grain and say it wasn't worth the money for me (if I had bought it-- I got it used from a family member for Christmas who also didn't get much use of it). I personally found that I stopped bothering with it after a month. Maybe if I was more active outside of work (e.g. if I took up running) I would use it more.
For me, I couldn't figure out much to do with it besides counting steps, monitoring sleep, and linking it to myfitpal. My phone's built-in pedometer seems to be just as accurate, and I always have that on me when I'm out and about. I did like how I could link it to myfitpal, but wouldn't have paid the full price of the flex to do so. The monitoring sleep thing is interesting at first, but I didn't bother much with it after the first few nights.
Also, it has silent alarms, but mine worked right only about 50-60% of the time! I don't know if that's because it detected my movement as tapping it, or if the silent alarm vibration hit right when I was moving and couldn't feel it. Or if it just never went off at all. That would've increased the value of it for me. I don't know if this is a defect in my flex, or what. I might investigate that.
I might give it another go for the sake of using it. It's just marginally more useful than my phone, solely because it goes on like a watch and can be worn a lot easier in some situations than my phone (e.g. if I'm doing things around the house I'm not usually toting my phone from room to room). The thing I DO like about it is that it serves as a reminder to be more active and make better choices. It does give you a little bit of a focusing point.
All depends on what you're looking for. I suppose it just wasn't what I thought I was looking for.