I can help clear this up once and for all.
Posting this on 12/29/19
On our birdmap, it will show that .0510 FCC mode is possible BUT...
ONLY if you had FCC mode working on .0400, then used DJI Assistant or DJI GO to upgrade your firmware to .0510.
This is the ONLY way to have FCC mode working on .0510.
If your bird came with any other firmware than .0100 and you try and downgrade with NLD and get stuck at 15%, then you are on "locked" firmware courtesy of DJI and currently NLD can't help you with NFZ removal or FCC mode.
If you are lucky and CAN downgrade with NLD to .0400 or below and get past 15%, then you are on good firmware and NLD is for you. You can downgrade to .0100 and remove NFZ.
If this is you, only use NLD to upgrade or downgrade firmware, DO NOT USE DJI assistant or DJI GO to upgrade or downgrade firmware. You will end up with locked firmware.
We are working on the firmware to unlock it. It is slow going, since all DJI firmware is encrypted, and difficult to unlock mods. DJI monitors everything we do and takes action in firmware to stop any NLD mods from working.