These days CrossDOSFileSystem also supports fat32, long filenames and even can parse MBR partition tables if you want to mount something else than the first partition. :-)
mfm.device is naturally not needed or used if you aren't using floppy disk. The filesystem handler uses whatever storage driver your mass storage is connected to if the mass storage is not accessed at a low level.
The biggest problem we have had is, that the most popular filesystem (PFS3 and its variants) and the second popular filesystem (SFS) never made it to the Linux kernel.
Just about everyone uses a flavour of PFS3 in their Amigas these days and it is a bit of a pain that we haven't been able to just mount hard disk images natively. Instead we've had to run a full Amiga emulator to transfer data to and from disk images or hard disks/memory cards, which eats into file transfer performance.
mfm.device is naturally not needed or used if you aren't using floppy disk. The filesystem handler uses whatever storage driver your mass storage is connected to if the mass storage is not accessed at a low level.