Hiya
The best thing with a gps watch / hrm is the live screen, you can see exactly how fast you're running, how far, your heart rate, while you are running along. It would be kind of wasted in a pocket
There's other stuff out there, I think Polar have one or two, and Timex.
I have a garmin 205, and i find it awesome, an amazing help with my training. 305 would be even better for the heart rate stuff.
Hope that helps
