I agree, I use GWX control panel and it keeps that under control, also I have not installed any of the telemetry updates. The only problem is MS keeps moving the goal posts and if you are not careful will install more updates and the GWX needs updating.
But I should not have to install third party software to stop the the producer of a OS I use updating it to another OS I do not want to use and also to stop them spying on me.
I have to go and sort out a machine at the weekend that have been up dated to Windows 10 and something have gone wrong and it will now not boot, so this person can not use their computer for nearly a week as I can not get there until the weekend. Thankfully they got stuff backed up they back up every day, but what about if they did not back up every day and they had stuff on that computer that is important?
I have nothing against Ms putting up a nag once a month saying that windows 10 is free and if you want it then click here, but to start to download the files and then install it without people knowing is just wrong.
As you said it is easy enough to go back to Windows 7, but when you do, install GWX control panel as going back do not stop it happening again.
I suppose there is one good thing that came out of this, you can now update to Windows 10 when ever you want on that computer even after the offer have ended, Which is getting closer and the sooner it ends the better, but be prepared for MS to go nuts in the last few weeks.
Desktop machine now powered by windows 8.1 pro 64bit, no dreaded metro, laptop by Linux