Backup & Restore EFS on your OnePlus One through ADB!
No TWRP Recovery needed!
UPDATED : MAY 1, 2018
YOUR PHONE MUST BE ROOTED
First you need to enable USB Debigging mode by checking Settings -> Developer Options -> USB Debugging. If Developer Options is not found, go to Settings -> About Phone and tap the build number rapidly 6-7 times till a toast comes up saying 'You're now a developer' (or something like 'Developer Options is enabled'). Go back. Voila! You see 'Developer Options' above About Phone in settings. - Thanks to @Heisenberg for notifying!
Just download the attachment, extract it to a folder, connect your phone to PC through ADB, double click on 'BACKUP EFS.bat'. When it says 'Press any key...' just press any key on your keyboard! You'll see 'modemst1.bin' & 'modemst2.bin' files in the same folder where you extracted the ZIP, make more copies and backup of it! That's your EFS!
Connect your phone to PC through ADB, place your 'modemst1.bin' & 'modemst2.bin' in the folder where you extracted the attachment (it should be there if you never moved it after backing up) and double click on 'RESTORE EFS.bat'.
Hope this helps someone