Have you tested it out yet? Was curious how accurate it actually was.
I havent had the chance to do any really playing with it yet. I did set it in the 0 to 30 mode for my ride home from work yesterday and when I came to a complete stop it auto started every time and it did seem to properly time how long it took to get to 30 mph - hard to tell how accurate it is without anything to compare it to, but it seemed okay to me. More important to me than being 100% accurate will be if it is consistent. if it is then I can use it to do before and after tests when I make changes to the Sling.
As a side note the apps author recommends getting an this external GPS receiver for increased accuracy XGPS160 Multipurpose Universal 5 Device Bluetooth GPS Receiver with Wide Area Augmentation
might be something to consider if one were going to be doing actual track testing, but for my uses I think the phones GPS will suffice
Just found this link that tests the accuracy of phone based GPS vs a dedicated GPS GPS accuracy tests looks like we are talking less than 2% error