I had mixed thoughts about using a Garmin 305 with the cadence sensor and heart rate monitor. I was skeptical that it would be nothing more than a toy. However, after a week of riding with it and looking at the data collected, I'm convinced that it will have some real value.
Here's what tipped the scale for me. In looking at my data I was shocked to see how often I stop pedaling during a ride. And with the graphs showing me just when, where and for how long I stopped, I realized my riding could be much smoother. This morning I went out with the specific intent of reducing the number of "non-pedaling" incidents that would show up in my data. With just this simple thing in mind, I've cut them in half and bumped up my average speed almost 0.6 MPH for a measured ride I do frequently.
I fully suspect that as I get deeper into the data (especially heart rate and time in specific zones), I'll do a much more effective job of keeping fit. OK, so it's still a bit for a gadget/toy, but a useful one!