Op op op:
http://blogs.windows.com/bloggingwin...review-builds/

As long as you are running an Insider Preview build and connected with the MSA you used to register, you will receive the Windows 10 final release build and remain activated. Once you have successfully installed this build and activated, you will also be able to clean install on that PC from final media if you want to start over fresh.

Znači svi Windows Insideri dobivaju Windows 10 for free!