i got prompted to upgrade to this today in my Windows 10. Despite what I'd seen here about the 2.1 incompatibilities with Windows 10, it was working flawlessly for me.
Now when Boxcryptor starts, it shows the key file, has "firstname.lastname@example.org" listed as the user (and it's grayed out). I type in my password & check "Remember password" but the "Sign in" button stays grayed out. There is essentially no way to use a local account, and I'm not going to switch. I trust nobody with my key.
Yes, I'm a paid user.