Just in case others are looking at this thread, I’d suggest avoiding the OnePlus 3 (and potentially 3T and 5) on security grounds.
I factory reset an encrypted OnePlus 3 before selling it, which should have cleared the encryption key and hence all personal and biometric data from the phone.
The new buyer was therefore somewhat surprised to complete the “new phone” Google set up process and discover several years worth of my text messages still in the messaging app.
Apart from the fact that it’s embarrassing (there’s an awful lot of my personal data in the wild now), it raises some concerns about whether the phone was encrypted at all. I know damned well that it said it was, because that’s what gave me the confidence that a factory reset would wipe the phone.