As with most things in life, the answer is "it depends." Apple has released the third incarnation of the iOS 12 public beta. But should you install it on your iPhones, iPads, or iPod touch devices?
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As with most things in life, the answer is "it depends." However, as the public betas mature, it feels like less of a gamble to install it.
I've been running the iOS 12 developer preview beta on test devices for since it was released last month, and my feelings about it continue to be somewhat mixed. I've gone into some detail about some of the issues here, but here are the highlights based on this latest release:
If you've got an older iPhone you can throw it onto to play with, then why not. If your only iPhone or iPad is also your daily driver, then my answer is going to be a resounding "no." Running betas on the device you're trying to use for real work is a great way to have you hating your life.
OK, so you still want the iOS 12 public beta. Here's how to get it.
If you want access to the public beta, you need to sign up for it. You can do that here. It involves downloading a profile to your iOS device (when Apple releases the final version of iOS 12 later this year, your iPhone, iPad, or iPod touch should automatically update to the final version of iOS 12, and you'll then be able to delete the configuration profile from Settings > General > Profile).
Before you go any further, you might want to look at my list of precautions and caveats related to running beta software on your iPhone (things can go from smooth to ugly in a heartbeat). At the very least I suggest you have a full backup of your device done (I recommend you make an encrypted local backup using iTunes).
If you do decide to run iOS 12 public beta, and later realize that it's making you hate life, you can uninstall it by following these instructions.