Inserting GPS data is always cumbersome in my experience.
Separate GPS-trackers like Solmeta drain their battery empty and the switch to the camera’s battery draining. Also, the tracker can write directly into the RAW (at least the Nikon version), but that means dedicated cables – and the Solmeta spiral cables were of questionable quality. Falling apart after 3 or 4 years.
Maintaining a WLAN connection between phone app and camera is also draining both device’s batteries.
Inside a building GPS often doesn’t work. Then it’s the phone’s capability to use known WLAN addresses as location tags.
Transferring iPhone or other cellphone’s GPS entries lateron is extra work and so far I haven’t found an easy way to do so, like copy & paste.
Sometimes it would be just enough if the camera registers one place and transfer this metadata to all following images until it’s moved 20 or more meters away (like a birdwatching stand), but apparently it’s more interesting for the manufacturers to put in 5 dozen different video modes instead of one useful GPS feature.
Personally I’d like the GPS stored in the RAW file, its’ a feature like storing the focuspoint/s, orientation of the frame, type of exposure meter and belongs to that image. When I transferred my Aperture libraries to Crapture One, I benefitted a lot of the way Aperture’s designers implemented “places”.