I have a Garmin 800 and it has a heart rate monitor. I think heart rate monitoring probably gives a a more accurate calorie burn. I also have used a Polar FT7. Both of these are lower end models but I love the Garmin for the bike because of the miles, the map. My experience with chest straps has been good, both Polar and Garmin. I think the Garmin a little thinner. They both fit right at the level of the lower band of a bra and are pretty innocuous. My heart rate runs 125-151 during rides. It is in the 145-151 range when I am working hard and I cannot sustain the effort that comes with that Heart rate for long. In the language of the Target Heart Rate, I would say that 145-151 is over the 85% of my maximum but since I am 58, all in all I consider that pretty darn good.
2011 Trek Madone 4.5 WSD
2011 Trek FX7.2--What can I say? It was on sale!