BodyBugg/BMF calories burned off??

GIBride01

I have a BMF BodyBugg as well as a Polar F5 HRM. My BMF numbers have looked lower than normal lately, so decided to wear both devices to my high intensity workout class last night. BMF said 342 calories burned, HRM said 623! I seriously doubt the 342 number from BMF..I have worn it in the past to the same class with much bigger numbers, closer to the 500-600 range. Anyone have problems with their BMF acting hinky as far as calories burned? And what did you do to address it? And anyone who has both prefer the HRM? I received the BMF as a gift with a 6 month subscription, which is ending in 2 weeks, don't really want to have automatic drafts taken out of my bank...but want to go with the more accurate device. Thanks!