Sure the sleep monitor is kind of cool, but to be honestly I tend to find it out of whack. I tend to switch between totally active sleeper (think running in my sleep) to log to laying there without moving for hours while suffering from an absolute random bout of insomnia. Sometimes Fitbit picks this up, sometimes not, and honestly I can't say that I've looked at my sleep metrics much after the first couple of weeks.
I will say that the guilt trip I get from not wearing it for a couple of days or for spending a few days totally sedentary while working seems to be pretty good, especially with the weekly report. It does give me a little push to try and be active for the next week. Being able to look back and actually see which days I was active and which I wasn't is good. So is keeping track of my weight and other measurements.
The thing is... most of what I use this for is not the hardware... and there is good reason for that. The location on my wrist tends to interfere with lifting gloves or straps. I have had it get caught on the lip of my chalk bag and either drop into my chalk bag or tumble 40 feet almost hitting my belayer in the face.
Fundamentally thats the problem with my Fitbit flex though, its really good at measuring a couple of things and mostly for running, and not quite so good at measuring the activities that I do. Now to be fair I have no idea how you would measure reps on a leg press with a wrist worn device. Or how the same wrist worn device could ever hope to tell how my clean my movement was while I was climbing (though some kind of altimeter in there would be kinda neat to tell how far I had moved up and down over the course of a day).
Some of this looks to at least be changing with the Alta. Being able to track my heart rate is far more useful to me than number of steps. It will give me some visibility into when I'm ACTUALLY working out hard and when I'm giving it a half assed effort. I may get some metrics into how hard a route or boulder problem actually was for me.
The band design actually looks like it may be helpful too. Having a latching band versus the one on the flex should solve my catch and drop problem, I also may be able to wear it a little higher up on wrist to deal with lifting straps. Plus I still get all the awesome things I use my current Fitbit for.
I guess what I'm saying is, come on April, and just go ahead and take my money now!