SO I have been using the insider edition of windows 10 for several months, and I must say its been ok. Still prefer xp or 7 myself, but 10 has been very stable. My netbook updated to the full release of windows 10 Pro a few days ago, and the only issue is windows defender is not working. oh well. I have pcs with linux, windows 8.1, 7, and Xp editions on them. I'll leave those alone for now.
I hadn't realised the offer had already finished - oops! Presumably at the end of July? I also didn't realise the prompt could be reactivated by adjusting the computer's clock but I'd already upgraded all mine when the offer was still new. The only ones I couldn't upgrade were a 2007 Vista Toshiba which I used to dual boot with Ubuntu Linux (until that got out of date more than I could be bothered to mess about with) and an XP Acer from 2003, 1024x768 'square' screen, still running albeit slowly!
Apart from the infernal, huge updates that still keep happening, Windows 10 has been OK for me but I'm not a demanding user and - apart from a 2004 laser printer that still works with a bit of faff - I don't have much old hardware or software.