However, there seems to be a loophole in Apple's implementation as discovered by ElcomSoft.
In my case checking the (beta) battery health feature in the iPhone settings threw no light on the abnormal performance, with maximum capacity reported as a (healthy sounding) 91%, as well a claim that "normal" peak performance was supported.
Elcomsoft engineer Oleg Afonin noted that testing showed that once USB Restricted Mode kicks in, there is no obvious way to break it.
Unlock iPhone to allow USB accessories to connect when it has been more than an hour since your iPhone was unlocked.
This chink in the USB Restricted Mode's armor can probably be closed, but it might prove annoying to users.
The bug is alleged to reset the one-hour counter available within the latest iOS update as long as a USB accessory is connected to the iOS device before the toggle triggers the lock. However, the iOS will reset the countdown timer if one immediately connects the iPhone to a compatible USB accessory. There are people who'd prefer unlocking their phones every time someone connects an accessory to the Lightning port instead of being subjected to the flawed restrictions.
However, if you aren't actually happy with the release, and you want to go back to an earlier version of iOS, then be aware that Apple is now only signing iOS 11.4, which means that you will only be able to downgrade to iOS 11.4.
It prevents specialist unlocking hardware made by the likes of Cellebrite and Grayshift from entering multiple passcode guesses via the phone's data port. Specifically, the update fixes a problem that kept some users from seeing the last known location of Apple's true wireless earbuds with the Find My iPhone tool.
With a power-transferring accessory, police - or other hackers - have a fairly straightforward means of accessing a seized iOS 11.4.1 device.
If the countdown expires, USB Restricted Mode is still a good defense against hacks.
Apple curiously didn't include the security in the release notes, probably to not alert "interested parties".
"We don't know if this behavior is here to stay, or if Apple will change it in near future".