[deleted] Assuming usb is set to "allow when unlocked" wouldn't that prevent a lot of attacks that are "cellebrite/usb" related?
Indeed that should help. The problem is that what Cellbrite etc. exploit are things that shouldn't happen, i.e., bugs.
BFU the owner profile file system key is not available for the kernel to do decryption. AFU the kernel can do decryption with the key (that's the point of unlocking). If the key is available and the kernel can be tricked into decrypting things, they will be decrypted.
Said differently: to get your bits AFU would require a bad bug. To get your bits BFU would require a really bad bug.
If your threat model (unlike mine at present, BTW) includes sufficiently resourced attackers and sufficiently grave consequences, then the BFU/AFU difference may be very significant, and the difference between a 6-digit PIN and a long random passphrase may be significant.