I was searching the net for this info last night, glad I finally found it. I agree the calorie burn is pretty low, but I started the program because I wanted to mix things up and add strength training to my usual running routine. I think it does a nice job of keeping things fun. I will say I completed Insanity right before starting this. If you want a better burn Insanity is the way to go.

Here are my calorie burns each time I have done the workouts. I am in transition week from block One to Two and doing the classic program. I am 5’4” currently 129 lb female.

Total Synergistics – 135, 101, 73
Cold Start – 25, 22, 21, 19, 29
Agility X – 169, 223, 193
X3 Yoga – 46, 43
The Challenge – 69, 98, 100
CVX – 296, 289, 251
The Warrior – 174, 147, 148
Isometrix – 63
Dynamix – 109
Accelerator – 196
Pilates X - 46

Week 1 Day 2 of P90X3. These workouts are wicked! and Tony is hilarious, as always.

Male
142 lbs

Total Synergistics = 454 calories, 31 minutes
Agility X = 493 calories, 35 minutes

I use the Polar FT-4 and it has worked great fot me. it doesnt have all the bells and whisles but it works fine for what I need. it tracks calories and heart rate.

I picked up an FT4 yesterday, and decided to give it a try. It takes a bit to find where the "tight enough" point is, so one tip I'd recommend is after strapping it on, go into a few different positions (plank, downward dog, etc) that aren't "standing", to make sure that it's not too loose at that time.

Anyway, I gave it a go during my Isometrics workout last evening (Day 1 of Week 4), and for the 30 minutes, my calories burned were 296. My heart rate was mostly staying in the 115 to low 120s, and hitting the 140s near the end of the pose when I was ready to fall over. My normal (not fresh out of bed RMR) rate is like 65-70.

I used http://www.shapesense.com/fitness-exercise/calculators/heart-rate-based-calorie-burn-calculator.aspx to compare, and the calculations were pretty close (I estimated 120 bpm, and checked the net calories burned link after).

It might also be that Yoga is still very new to me, though I'm getting better at it, so it takes me a considerable effort to do the work.