I have one!
I wear my Fitbit every day and night (for the most part), it has sort of become part of me. The best thing about it IMO is the online dashboard thing. Since the Fitbit sincs wirelessly (super cool) I just look at my dashboard daily to see my calorie expendature and what my allotted calories are for the day to reach my weightloss goal. When you set up the dashboard the first time, it takes your height, weight, etc. and figures your basal metabolic rate (how many calories you burn per minute in a resting state). You choose your desired weight and it gives you options on how quickly you want to lose weight (ie cutting calories/pounds per week-- easy, medium, hard, etc), then it calculates how many calories you can eat based on your BMR and your activity level throughout the day. It can even "learn" your habits and make projections on your calorie expenditures as you wear it over time.
It sounds complicated but it makes it super super easy. You just plug in a few numbers and the online dashboard does everything else for you. You can also track your meals, fluid intake, sleep patterns, weight, and exercise on the dashboard.
For the most part, I use my fitbit to see my calorie expenditures for the day and how many calories I'm able to eat to stay on track. My job is fairly physical so I was very interested in seeing how many calories I burn on a day-to-day basis just at work, not even including workouts. I was having a very hard time losing weight but have been much more aware of my intake/output since getting my Fitbit. I am losing slowly, but surely.
By the way, I just use the free dashboard-- I don't really see a reason to upgrade to the premium.
I clip my Fitbit to the center of my bra. There are only a few outfits where it doesn't work very well to do that, so I just clip it on my pants. I even wear my Fitbit to tennis, just clipped on my skirt, with no problems. The Fitbit itself is just about the size of a flash drive and can clip onto something fairly thin, but it has a little plastic carrier beltclip thing that you can slide the Fitbit into that allows it to clip over thicker things.
Sorry for the long post. Feel free to ask further questions or PM me if you want. I love my Fitbit!
Not all who wander are lost.
Fine and thin 3a. PW: curls