I have the 400 and I love it. One of my favorite features is the altimeter; it's very cool to look at the graphs after I ride and see just how steep that "monster" hill was And then see how much my heart rate spikes on said hill I don't pay much attention to the HR percentages, but I know you can set your own "zones" or use pre-set ones. It also supports cadence, but doesn't come with the sensor, if that's something you're interested in.