First off, I'm on Project Fi, and the Android N beta worked fine with Project Fi for me (Nexus 6P). Unenrolling was painless for me, just followed the "unenroll" link here:https://www.google.com/android/beta
The worst part of trying out the beta was getting all my settings back to where they were before I tried it, when I decided to come back to Android M. When you unenroll, the OTA that you get is essentially a ground zero start (factory reset). Then restoring from google gets you all your apps back, but not all their settings. And then you have to go through the phone's settings and make sure everything's set up as you like it. Didn't take that long, but almost made me wish I'd stayed with the beta *smile*. Or that I was rooted so that I could just restore a nandroid backup.
But it was an interesting process, and Android N looks like it's going to be good.