I use Cyclemeter exclusively, after retiring a garmin edge 800 with its own speed/cadence and hrm sensors. The GPS speed is not the greatest even under best conditions, but my distances are very consistent even against fellow riders' standalone computers. My plan is to buy a bluetooth speed/cadence monitor in the future for a more accurate measurement, but for the past couple of years I've been pretty content with what it does (for free!).
If you are using an iPhone 6 or newer, be sure to check the "use barometric altimeter" in Cyclemeter settings. iPhone 6 and newer all have onboard barometric altimeters that even with cases on seem to be extremely accurate. Even in airplane mode with no cell connectivity it will display very accurate altitude and grade readings. This could be a feature included only to premium users that I've inherited as I did pay for the 'elite' version one year that I've since canceled.
Last edited by EricSteven5; 08-19-16 at 02:29 AM.