Honestly, that's why it's called a Beta.
They release to developers or to the public, it's still in a work in progress with many parts working but parts still in development. Because it's still in development/testing, it's most likely they are releasing it with a list of bugs they are aware of but working working on patching and be in the next release to test even though by the time it gets to public release it's hopefully more stable than when it was only a private release. I think they even tell ya it's gonna be unstable when you enroll in the beta.
You are testing whether those fixes work and if not... back to the drawing board until they have gotten the OS to the point of going Gold. You > Beta tester = Guinea Pig.
Yes, if like iOS beta program, if you enroll into program, you have to unenroll to leave the program. iOS is easier to go back to normal because if make a iCloud backup of your phone before beta, you just erase the phone after unenrolling and choose to restore the pre-beta backup.
No Pie available for Note 8 but honestly not sure I'm that excited about One UI. Concerned about what features Samsung will decide to keep in and carry over to Pie and what features we end up losing.
Once I see that Gear works and other bugs fixed then I'll go back to it. I can't see how they would release a beta without something so basic like Samsung Gear and Samsung Plus not working.