Another very happy upgrader here......
I bought
a single PC activation code from Ebay for Win 8.1, (about 12 and a half quid

) mounted the ISO and installed it, no probs, though I didn't bother playing with or even updating 8.1 as I've used with it on another machine and fucking hated it.
So I went to the W10 update site, created another ISO (on a USB stick and on DVD just in case) and updated from the ISO on a spare drive......20 mins later, it was done.....amazingly smooth for a new OS install
I'm instantly at home with W10.......ok, there are some differences but finding stuff is intuitive rather than fricking frustrating like it is with 8.1
It's recognised and installed nearly every device I run.....Logitech 430 headphones, several USB hubs and a PCI SATA expansion card from which I hang three old HDs in addition to the MB controlled ones (8TB yayyy!) .......I've had to reinstall the Logitech gameware for my MMO G600 mouse but I was expecting that.
The only thing W10 doesn't like is my Madcatz S.T.R.I.K.E 7 keyboard, which was a bit of an issue 'cos I use it as a clock, app launcher, sound controller and I run a bunch of macros on it......I've just got it working properly though by reinstalling the W7 in compatibility mode as Admin, and I have my profiles, app launchers and everything else back
W10 even recognised my three screens and set them up properly, although I had to use Nvidia control panel to place them in the correct location and designate the primary screen (47 inches of 1080p gorgeousness!)
Now I'm going to play with Cortana, but I doubt I'll actually be using her much......I like the Zen silence of decent headphones and a top KB input too much to be talking to an imaginary AI friend