One of my friends has one and she's not so sure it's all it's supposed to be.
I've also seen some saying there was some sort of reaction some had to them and they had been recalled.
So, after saying all that. I'm sure the people who are designing it are constantly refining and and upgrading it. I think if you do your research and figure out which model or style will best work for you then it would be a good thing to have.
One thing I will suggest to do to supplement it, to verify it's accuracy, is to do the stuff on sparkpeople.com.
sparkpeople.com has a program where you can enter in every single thing that goes in your mouth, from a Big Mac to a piece of Double Bubble Bubblegum. It breaks down the information into usable data and the program will even help you design an exercise plan to meet goals such as "increase your cardio by 20 minutes and increase weight training by 15 minutes". It's a good program.
I'd use both to see if the information is similar or way off. sparkpeople.com has been around a long time and I'd trust it when comparing how many miles I've walked and one says 1 mile and the other says 5 miles...