I updated 2 laptops (both were purchased around late 2014) to W10. One went really well but the other I had to revert back to W8.1 because the Wi-Fi stopped working. I don't know who is to blame for the failure. I'm not too bothered as I'm reasonably happy with W8.1 ...
I think non-techies users who were forced to upgrade to W10 in the belief that it's better than W8.1 might struggle to revert back to W8.1 when things go wrong with the upgrade process or hardware.