I’m running the developer betas. My experience is that iOS 12 beta is very solid. I’ve not run into any issues that get in the way. Not crazy about the change to the camera icon in Messages (explained in this tweet), but that’s design, not a beta issue.

As always with beta software, make sure you have a solid backup (in iOS, make sure you archive the backup, so it doesn’t get overwritten) before you make the move.

Here’s the link to Apple’s beta program page.