Just to check (as I may do that this weekend), when you say 'restore as new' is it still ok to restore using a backup?
Not any kind of backup restoration, only synching via iTunes as you'd do with any new iDevices.
I, as I've pointed out previously in the thread, never restore. This is why I've never ever had any kind of battery problems (apart from hardware issues) otherwise plaguing iOS.
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The problem is that betas will expire.
Nope, if you spoof it. See my thread at https://forums.macrumors.com/threads/1688804/
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I'm also having crashes with iPad Air due to low memory. My iPhone 5S on the other hand seems to be working just fine.
Yup, it was a big mistake on Apple's part not to add another 1 GB of RAM to the new iPads. They, because of the much higher-res screen, use a lot more RAM for the same task as on an iPhone; particularly WRT web browsing.
The situation is even made worse by native 64 bit apps' / widgets (Safari and UIWebView used from apps specifically compiled for arm64 both belong to here) using significantly more RAM than in 32-bit mode. (And the latter - 32-bit - in only available in third-party apps not compiled for 64-bit. The built-in apps are all 64 bit, incl. Safari, which means you in no way can reduce their RAM usage, unlike with third-party apps, where you deliberately can go for a 32-bit one to reduce RAM usage.)
Planned obsolescence - all too common with Apple's products, regrettably.