We are currently using zerocopy.
It is quite handy and convenient, but maybe not the ultimate answer.
Note that we mainly read, but we could totally offer rich writing capabilities, e.g., given raw raw files to build directories from.
The caveat is that we can't do much, really, since ME directories are fully signed anyway. Unless you are the OEM or otherwise somehow get to deploy custom ME firmware, that is.
Other crates to look into: