I'd rather use something that works with block device directly, rather than something that depends on the filesystem code and may lead to filesystem corruption and potential for kernel instability. Also it seems like a weird design decision to fill flash with files, when in Linux there's trivial access to block device directly.

It's also possible to write 64bit address of each 8 byte block to every such block, and avoid pseudorandom generator, and potentially have more insight to what happened when the block ends up mapped to unexpected location.