I thought it was going to be free? I'd try it out if it was. It's always handy to have a windows machine and a cheap pi would be great for this. Certainly not going to pay, though.
I was under the assumption that only the upgrade version would be free and that only those with existing versions of Windows 7 or 8 can upgrade to Windows 10 without cost whereas everyone else would still need to pay for a full copy.
EDIT: Yup, it seems I was right:
Windows 10 will be a free upgrade, but only for the first year of its existence. That includes upgrades from Windows 8.1 and Windows 7, along with smartphones running Windows Phone 8.1. Once you’ve updated your device, Microsoft says it will keep the software current for its "supported lifetime."
Link:
http://www.technobuffalo.com/2015/01/21/windows-10-is-a-free-upgrade-for-just-one-year/If you are running Windows 7 or Windows 8, you should already have had an invitation to "reserve" a copy of Windows 10. If not, run Windows Update to see if any updates are available for your PC. The one you want is KB3035583. This puts a small white Windows logo – the GWX or Get Windows 10 app - in the system tray on the right hand side of the Taskbar. Alternatively, you should be able to find the invitation by going to Windows Update in the Control Panel (via System and Security).
If you are running Windows XP, Vista, or any other version of Windows then you will not get a free upgrade offer. However, you will be able to buy a copy for a maximum price of $119 (Windows 10 Home) or $199 (Windows 10 Pro).
It remains to be seen whether Microsoft will offer launch discounts to XP and Vista users. I wouldn’t bank on it. Such users have already ignored cheap upgrade deals for Windows 7 and 8, either of which would have got them Windows 10 free.
Link:
http://www.theguardian.com/technology/askjack/2015/jun/04/microsoft-windows-10-free-upgrade-10-questions-answered
