The core functionality (distance and heart rate monitoring) works perfectly. There's none of the signal drops I've had with other heart monitors. Once the satellites are initially acquired, I've only had one dropout when I was outside. The initial acquisition of the satellites can be quirky and can take some time. The accuracy (according to the readout) is +/- 25ft, depending on how many satellites can be found. I've compared the distance measurement on the GPS with a known, measured distance on one of the trails I run on (the Chicago lakefront path). The GPS always increments a mile when I'm within 5 or 10 feet of the mile marker sign on the path. Well, I guess that's the least I should expect from a $350 GPS unit! Of course it's bigger than a normal running stopwatch, but that hasn't bothered me at all. The heart rate strap is also very comfortable and well-designed.
The display is crisp and has one outstanding feature: The information presented on the various pages can be completely user-customized. The default screen layout is rather poor, but in just a few steps I could replace it with the information I wanted to see while I run. There are almost 40 different data fields you can choose from for display. Examples: current pace, average lap pace, average run pace, heartrate, distance.