When I was personally using it, along with my clients, it was called BodyBugg. I had three of them (got them through the old gym I worked at), and from my personal experience, the device is pretty accurate. when you downloaded the info onto the computer it would give you your calories expended throughout the times of the day, so you’d visually know when you were most active. The software also allow you to enter in your nutrition.
For it to be very effective, you’d have to wear it throughout the day, and even in your sleep (that’s what I did because I’m a fitness freak), but I’m sure my clients didn’t and most people wouldn’t either.
I’ve been using it with clients since 2002. It is very accurate when set up correctly. But, the biggest thing it can bring to the table for you is often the missing clue. I’ve had clients that record their calories “fairly accurately, but still don’t lose the weight..” This device can either show you that they are not recording correctly, or that they have “killed their metabolism” with too few calories, long fasting periods, over-training, etc; and are not burning very many calories when they work out because of poor nutrition or the need to kick in some F.I.T.T. principal modifications to their routine.
It also serves as a constant reminder for them to make the healthier nutrition choices and do a little more activity. Having the device present on their arm and receiving constant updates via the watch or smart phone reminds them all day that they are working toward a goal that often is forgotten about when focused on other things such as work.
I have several people using it now. I recommend it for the clients that need the extra help with accountability or “the missing piece to the puzzle”..