Blu_Spark TWRP updated on the OP 
Sure you can unlock bootloader.Can I unlock the bootloader while I am on the open beta 4? Or should I go to a stable build and then unlock the bootloader
I assume all that can be successfully done on stock OOS 5.1, right?Twrp will be replaced by the stock if you boot on stock kernel on stock OOS.
You need to flash root or custom kernel like blu_spark to keep twrp.
So flash twrp, reboot twrp, flash root or custom kernel, reboot system.
Sent from my oneplus3 using XDA Labs
YesI assume all that can be successfully done on stock OOS 5.1, right?
I try unlock bootloader from rom beta 4 don't working..Sure you can unlock bootloader.
EFS is the partition with your IMEI numbers where nandroid backup is the backup method which can backup those partition(and any other partition).What's the difference between Nandroid Backup and EFS ?
Format data and type yesSo I have tried 2 times to decrypt my OP5, formatted in TWRP and flashed no verity OP5 zip and flashed magisk and I'm still encrypted wtf.