Hey Joe,
I installed iOS 12 two days ago in my 128GB 6+. I skipped iOS 11 because of all the issues folks seemed to be having.
So far, so good - apps launch faster, Apple Pay works, Touch ID unlock works mush faster, WIFI and LTE connections seem good. The only problem I've found so far seems to be related to an app that needs a tweak for iOS 12. The overall interface has changed for me a little from iOS 10 but nothing spectacularly different.
I also had some weird intermittent issues that required restarting my phone. Apple suggested that I backup my phone and do a Reset to try to fix it. If that didn't work they thought that the next step was to reinstall the OS. You could back up one of your phones and try installing iOS 12. If it doesn't work for you then you could then restore it back to where you were. My issues haven't shown up since I installed iOS 12 - but it's only been a couple of days.