I updated directly from ISO. All went well... Thus far xD
In Windows 10 Insider Preview build 10122, Start no longer has the expand or restore button at the top right corner of your Start menu. Instead, you can now turn on or off to use full-screen Start in the Settings app.
See: Start Full-screen - Turn On or Off in Windows 10 - Windows 10 Forums
I have no idea about download links on unofficial leak sites like those in Wzor's tweet. Never tried one, will never try.
First thing I checked was nvidia driver for GTS450 which had been constantly failing on update - latest driver is now present and correct Whoopee!.
Onwards and upwards