I have had one for about 9 months now, and I have mixed reviews. First off, I don't think the display is worth spending the money on. It never matches what the armband says when you upload it to the computer. Sometimes, there is a 200-300 calorie difference. I've called customer support several times. All they can tell me is that they are trying to fix the issue but until they do, you should believe what the computer tells you because it's more accurate. Therefore, I do not see the point in having the display. Next, I have been through 8 armbands in the 9 months I've had it. The velcro constantly comes off. Again, customer support is aware of the issue, and if it happens to you, they are very good at sending out free ones to replace the broken ones. I love the way it tracks your sleep, and I'm constantly amazed by its accuracy in that fashion. I have not lost a single pound since using it. I track everything I eat, and I always have a 250-500 calorie deficit, and nothing budges. I do like using it when I'm working out because the treadmill will say I burned 600 calories, and the GWF will say something like 400.
To me, I say you get the same benefit by using a free program like Sparkpeople.com to write down all your food.