As of 10 minutes ago now running a 6660. The MAC activation was suprisingly painless... 5 minutes waiting on the phone, having someone who actually understands when I start telling them my story of Adam, Bertha and Ceasar, afterwards pluggin the damn thing in and everything just worked™ for me too (sorry, had to steal that).
Did not expect that at all, after they told me it could be 2 hours (I guess just to be safe so people don't call again 2 min later) and after they fucked up last time (3 years ago) entering a misunderstood address and refusing to fix it over the phone, insisting on a technician (who facepalmed when we told him exactly what the issue was, but knew who to call for a fix).
After using the same Wifi settings I don't even have to re-connect any devices manually (I did not think that would work tbh), except for the two fritz1200 repeaters (yeah I'm cheap) that I have to run.