You can quickly switch between Open Beta and stable version. Just right click on DCS shortcut on your desktop and add this:
If you want to get back to stable, release version just change @openbeta to @release and you're all set.
Why would you want refund? Of course they want to test first Viggen first by catching and fixing all major bugs, before initial release to wider audience. Dev mentioned also some functions which are available in Viggen, work only in 1.5.6 so it all makes sense.
If you are also so disappointed just wait week, Viggen will be available then in release version.