Rushfit Calories burned

I recently purchased a Polar heart rate monitor to get an estimate of my calorie burn during workouts. It seems accurate (heart rate it gives is accurate and it's calories burned are less than cario equipment, but seem reasonable). I have work the heart rate monitor during 2 Rushfit workouts, and it indicated I burned 381 for one work out, and 371 for another one. These are very intense workouts, with my heart rate generally above 160 and into the 180s (I'm 42). Given the nature of the workouts, do these numbers seem like a realistic estimate, an overestimate, or an underestimate?