iPhone heart rate apps

amerrill1

I use an iPhone app on my 4S that uses an "ear clip" (I don't remember who made it) to "monitor" my heart rate. I ride my mountainbike w/ my son and my dog every morning at a park near our house. From the time we leave the house to the time we get home, is probably about 45 minutes. My bike computer reflected a ride time of 35 minutes (after water and resting breaks from my son and dog). The app (GOtality Express) reflected a calorie burn of 606. The activity I would have used on MFP reflected 426 (I only entered the actually ride time of 35 minutes). How much comfort and reliability can I put on the heart rate monitor app? Or would I be better off using MFP numbers. Thanks!