YOU CANNOT CLEAN INSTALL INITIALLY OTHERWISE YOU PASS UP YOUR FREE UPGRADE
UPGRADE TO WINDOWS 10 VIA WINDOWS UPDATE OR BEGINNING THE WINDOWS 10 SETUP WITHIN THE WINDOWS 10 DESKTOP. THIS WILL REGISTER YOUR DEVICE AS A WINDOWS 10 DEVICE AND YOU MAY THEN CREATE A RECOVERY DRIVE AND CLEAN INSTALL.
From my extensive testing of the new Microsoft Product Testing introduced into Microsoft Windows 10 RTM I can tell you the following:
Direct clean installation from Windows 10 Installation Media, skipping product key twice or using the generic key leads to an unactivated product.
Using the .iso to upgrade from the Windows Desktop will only allow activated versions of Windows to release the license agreement screen. This only allows Activated versions of Windows 7, Windows 8.1 or Windows 10 Insider 10130.
For Windows Insiders Windows 10130 is then updated to Windows 10162 via Windows Update and this is updated via Windows Update to Windows 10240 (RTM) .
Once the initial upgrade to Windows 10240 is complete the device is registered to Microsoft as a Windows 10 Device.
Once a device is registered, you may create a Recovery Drive and Clean Install.
The Recovery Drive may be used on other devices but you will encounter Microsoft Product Activation issues if the device isn’t initially upgraded via Windows Update and Registered as a Windows 10 10240 RTM device.
The product activation is tied to the device. You can reinstall using a different Microsoft Account or Local Account and the device will activate.
You may change minor hardware such as a SSD/HDD and clean install. I changed from a SSD to HDD for a quick test and Microsoft Product Activation was applied.
It seems Windows Insiders with Build 10130 will be passed as eligible to reach Windows 10 RTM even those who lacked a Windows 7/8.1 Base license. Those who look to join the Windows 10 Insider program after the Windows 10130 .isos have been removed will not be able to install and activate Windows 10 Insider 10240 RTM.
Windows 10 Build 10240 should be offered via Windows Update for Windows Insiders follow the instructions here:
Windows Insiders may leave the Windows Insider Program once on Windows 10 RTM as demonstrated.
There is no expiry date. no watermark on the desktop and it says Windows 10 Pro in System. The EULA does not mention prerelease software.
After the Windows 10 Upgrade via the Store you may use the inbuilt features to create a Recovery Drive which can be used to clean install Windows 10 Build 10240. The Recovery Drive can be used to install Windows 10 Pro RTM on another Device so appears to be generic Windows Installation Media Locked to an Edition but if the device has never been updated to Windows 10240 via Windows Update you will encounter Microsoft Product Activation Issues and be prompted to buy Windows 10. I tested a Recovery Drive created on a Windows 10 Build 10240 VM on a Latitude D820 with Windows 10162 and encountered the Microsoft Product Activation issues. See here for details: