Nit pick, this is a 256TB SSD, so you’d need four to make a PB of raw space, and probably more than that to allow for RAID and effective space. PBSSD is their name for tech to enable PB scale arrays of such SSDs.

The primary function of the app is to record a GPS activity with your phone. If you already have a GPS watch and like using it, I don’t see the point in using both. And I’m not sure about Coros, but Garmin at least give you the option to manually download your GPS traces directly from the watch without using their web services if you’re concerned about privacy.