Do people really do that?
I mean, if you're stupid enough to think the cheap plastic on your arm is as good as a lab in terms of accuracy and you use it to say "I've walked five km so I can now have a doughnut" then I'm guessing you're going to have a lot more problems in life then a few extra calories..(such as what to do with your collection of bridges)..
Precision in these devices is not needed, they're to show trends to promote action - oh, I've not had enough steps today, I should go for a walk.
There should be a body that independently verifies these things, just so consumers know at least the level of inaccuracy to go with - I also question how many devices were used from a provider in case they got the one made on a friday arvo.