Hello, I am looking to upgrade to a Mini 3 with the RC controller, but wonder if the RC is worth purchasing  with respect to it needing an internet connection? If it does need an internet connection, I assume it needs tethering to a mobilephone so that it can set its RTH and accrue data fr the flight path? Thank you.

Flown mine for 2 hours now without internet connection.   Unless you want to unlock a geozone no internet needed.

You can also pre-load map of the area you plan to fly in using wifi. but if you move to another area , you'll need to tether to your phone for update.

Hello there Dwarfii. Good day and thank you for reaching out. You can use your DJI RC to fly your DJI Mini 3 Pro without internet connection required and as posted above you will be needing internet connection when unlock a geozones, pre-load map and update the firmware of your DJI RC. Thank you and keep flying.