My experience, after wearing Band everyday since Xmas, and working out both weights and cardio, is that it does pretty good job of tracking calories burned and HR during workouts. I average 5 days/wk workout schedule between weights and cardio types.
While its true that pure cardio gets the HR up much quicker, using resistance such as weight also do the same job. Unless one is taking a very long break between sets, the Band tracks the tempo of lifting by measuring HR and showing graphically as it track (after syncing).
When I do elliptical or stationary bike, the measured calories are much higher than just lifting but in reality, that makes sense since there are lots of highs and lows in terms of HR. It also tracks cross-fit/interval type of training pretty well. Band measures the spike in HR and keeps up with all the activities accordingly - mixture of resistance/sprinting/isometrics.
About the only thing I haven't done with Band is actual jogging/running and outdoor bicycling. Plenty of stationary bike and treadmill at the gym but not outside, as I tend to do more of crossfit type of workout and weights than just running or bicycling.