Except for easy test confirming compression is taking place (so probably not an urban legend) I cannot tell much more. As this is very undetailed ground, who knows, maybe there is a HW solution Nokia implemented for compressing rootfs on the go and it should be(is?) faster. I definitely did not say it is slower by using CPU time (probably should have, seems logical), there might be a compression chip doing it (slowness could be introduced by it or by use case, 10kb txt file could go faster maybe, no idea, but microb starts faster for me from opt so that was my conclusion)