Based on my workouts, I don't think its too far off. I don't think its accurate to the calorie, but I think when I workout and communicates that I did 500 calories in my workout, I'd say that's in the ballpark.
I found my results to be as much as 20% above or below when walking the exact same distance. I do not know how many calories I used but it should not fluctuate 20% for the same 30 minute walk covering the exact same trail in the same amount of time. There were times that it did match a previous walk quite closely.
I am back to wearing my AW and look forward to the AW2 in March!