I don’t make use of the recycling program for the Fairphone 2, because I keep it as my backup phone, and I didn’t plan to make the Fairphone 3 my daily driver phone immediately for the initial lack of a Fairphone Open OS or LineageOS, but I switched anyway mainly because of 2 points that really stood out for me when I checked whether everything was working:
Mobile network reception for me is much better with the Fairphone 3, especially at home or indoors in general.
I don’t have software or hardware problems with my Fairphone 2, so the Fairphone 3 can’t improve that aspect for me.
Regarding the OS … there are ways to deactivate and replace a lot of Google stuff, so I make do on that for now …