We found that runners that use their smartphone to track their runs do so for less than a year before they buy a GPS running watch--or they quit tracking altogether. Reasons for this include accuracy, ease of use, and types of trackable metrics. Make no mistake, a smartphone will never match their ability to keep accurate data that you can conveniently access when you run.
If you want to continue keeping track of your runs but are tired of dragging your smartphone along, then you’ve already made the decision to get one of these. Next time you observe runners at the starting line of a marathon, notice how many have them on and how many are fumbling around on their smartphones.