I have the Fitbit Charge HR that tracks heart rate. I like it for cardio because of the heart rate tracking. I'm sure it's not 100% accurate, but it's close enough for me. I've compared the calorie burn from my Charge HR to the calorie burn in the workout manager, and they are usually pretty close. I find the step count is a lot lower with the Charge HR than the Fitbit One I used before. I switch to using the One when I want a more accurate step count but am less concerned with heart rate. I usually get ~4000-6000 steps on my Charge HR for 40+ minute Cathe cardio step workouts. It will track heart rate for weight lifting workouts, but my understanding is that is not a good estimate for calorie burn when lifting weights.