I thought I'd give it a try on my laptop - I doubt it could be worse than 8.1, but they aren't making it easy.
I have a legal, activated, and fully updated Windows 8.1, but it wouldn't display the Win10 update app. I spent one evening doing everything I could find to see why it wasn't working. I confirmed my license was OEM and not volume, and that I had all the required updates, but the Win10 Troubleshooting app said that it was not compatible with my system.
The next night I have up and decided to "refresh" my Windows, which uninstalled all my programs and rolled me back to 8.0 (what shit that is). That took hours, then there were a hundred updates that took still more hours. I managed to start the 8.1 download before going to bed, and got it installing before going to work. When I got back home, there were still several more updates to perform to get to where I started, but after the last the Win10 update app finally showed up. Gee, thanks for that lovely "Windows Experience", Microsoft.
Now it's two days later and I assume it's downloading in the background; at least it says it is, but I don't see anyway to check the actual progress. I'd like to charge them about $1000 for my time and aggravation - "free" upgrade my ass.