What do they use for actually recording the GPS tracks? As we can probably agree the built-in workout app sucks for the serious runner. And I never saw any goo

What do they use for actually recording the GPS tracks? As we can probably agree the built-in workout app sucks for the serious runner. And I never saw any good assessments of the GPS quality of the watch even though I've looked, do you know of any online? Now that watchOS 4 can connect directly to Bluetooth sensors, I'd be very interested in a GPS app that derived pace and distance from a BT footpod, much like you can do with a Garmin to get better accuracy.