I did an upgrade, then downgrade over the weekend from 4.2.5 to 5.4.1. My users did not like it, and were not shy in telling me that. That was after I put up a demo board for them to try and let me know.
I opted everyone out of the newsletter running this query in my user table:
UPDATE `user` SET `dbtech_newsletter_receive` = 0
Now they have to Opt In for receiving the newsletter instead.