HRM's can be quite motivating. Just keep in mind that they tend to be very accurate for well-studied cardio exercises like running and cycling. For other cardio, expect some errors. HRM's are for cardio exercises only, and not useful for anything else. Typically an average Polar should be OK, unless you want to work out outdoors and need a GPS. I have a Garmin 310xt that I love, equipped with a GPS, and pretty good at tracking the calories burned running or cycling.