Here are the features I love:
- Tests your fitness level, sort of like a VO2 max although nothing is ever going to be 100% accurate when it comes to that
- Use fitness level, age, sex, weight to determine calorie burn
- Stores data for you on workout time, average heart rate, max heart rate, and calories burned
It does way more than that, but that's all I use it for. I bought it because I read reviews and people seemed to think this was the most accurate calorie counter on the market. Of course, this was pre-Body Bugg. I wonder though if there are still Polar diehards out there! If you're looking for a fairly simple to use HRM, I highly recommend the Polar F series HRM's. From what I hear, the lowest level is fine if you're just looking for calorie counts and heart rate.
Another perk is that Polar has great customer service. My watch broke a year after I bought it and they sent me a brand new. Easy peasy! So if you find service to be important, that's another reason to go with Polar!