I just got this and I on Day 5 of the 30 day challenge. I do not know how accurate the calorie count is, but I do know if you really work at it, that it shows you burned more calories than what it projected, so who knows.
It may be wishful thinking, but after just 5 days on this, I can see a small difference in my arms and waist, being a little smaller. We will see.
I just finished up day #8 of the thirty day challenge and think that I can see/feel a difference, too. I have no idea if the calories are accurate or not. I do think it is of more use for toning than for cardio. It is nice b/c you can get a lot of exercises in in a relatively short period of time. Both my kids are young and I can find 20 minutes a day to fit this in when they go down for the night. I don't always have much more time than that.
My calorie count was usually lower than what the game said. I did have one day when it was higher though. I did not have a HRM when I was doing the challenge. I got it later & was using it on prepared workouts.