I'll have to reply again when I have more time. I took my 6D2 to Russia in Sept of 2017. 17 day trip traveling from St Petersburg to Moscow. 700 miles by boat. I used the GPS built into the camera. Worked well, had no problem acquiring a GPS signal. Have had the camera to Europe 3 times. England, Holland, France, Germany, Switzerland, Italy, etc. Worked great.
Camera or App - Wil be one or the other. If the camera is GPS capable, this will be embedded into EXIF data. If you are using the App, data from its GPS will be Embedded. They don't "share" or compare. Its one or the other. So if your phone can't get a good GPS signal and determine your location, you may not get the geo-tagging. My vote is stick with the camera.
Bay Area - CA
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