I have the Polar F6 because I needed a new watch and DH was convinced I didn't ride as hard as I felt so why not get a HRM? Still I haven't really figured it all out but I do know I ride in the right zone for weight loss but am anerobic when running. Yet I never lost weight cycling and did lose a boatload running. Like I said, still trying to "listen to my heart" but Polar seems like a good brand without dropping a ton of money.