Just some generic comments about the Flex to add to this thread
Comfort wise: very comfortable. I don't notice that I am wearing it. Compared to the Jawbone Up, it is more pleasant because it doesn't catch or bump anything.
Ease of wear: This is where I have been less enthusiastic. Two issues. One is that it has to be disassembled to charge the unit. I went ahead and did that overnight and forgot to reassemble it, so yesterday I actually wore an empty bracelet the entire day before I realized that I forgot to put the unit back in. The other is the clasp. While Fitbit makes a point to say that it is waterproof and can be worn in the shower or swimming pool, I've been taking it off so I can keep the zip and flex on fair footing (I don't give the flex extra steps by wearing it longer). Getting it back on is pretty tricky as it involves squeezing two little prongs into small holes that look like they belong to a minimalist wristwatch. You have to line things up very neatly and use a pretty firm squeeze in a tight space. As I use it more, I feel like the holes have a little more give, but it is still a bit of work to put on.
Anyway, my failure to reassemble the Flex yesterday makes it impossible for me to give a head-to-head comparison. I did get 9,478 steps, so my guess is the Flex would have given about 8120 steps had I remembered to wear it - and considering I was doing 'normal' activities.