My early experiences with Ubuntu were equally dodgy. I wanted to use wifi with WPA but in those days Network Manager did not support anything but WEP. I had to manually install and configure wpa-supplicant and its daemon (this was before systemd) and set up the interfaces. Every time I reinstalled Ubuntu I had no wifi, so I had to keep manually configuring. Eventually I tried an upgrade in place (this must have been around 2009) and it worked OK. It wasn't long after this that Network Manager started supporting WPA/WPA2 so everything worked out of the box whether you did a fresh install or upgraded in place. Of course, I moved on to other distros after that.

As a fella who had tried to upgrade Ubuntu installs in place a few times, with less than expected outcomes, I was quite skeptical of the Debian claims.  But too many people had extolled their successful upgrades for me to just dismiss them, so I wanted to give Debian a fair shot.  I was pleasantly surprised with the ease of upgrade.  I'll continue to monitor point updates in my VM and if Debian continues without any hiccups or niggles, I will be downright impressed!  And I'm a little more inclined to believe the claims now!  LOL!