[gentoo-user] Gentoo SDcard updates tactics

Hi,

There are two SDcards of the same brand and model.
The first one cariies a not so current Gentoo Linux.
The second one is empty.
Now the first one is image-copied to the second one with dd,
which copies the contents of the whole device (not the partitions).

Then the first one is put into my embedded system, boots up and
the normal eix-syn/emerge/compiel is done to update the system (whch
takes a longer time becaus this is an embedded system).

Will I get a technical identical working and valid copy of the first sdcard onto
the second sdcard if I rsync the relevant partition of the first onto
the second sdcard.

Or will I produce crap this way? Is this valid Gentoo-wise?

Thank you very much for any help in advance!

Best regards,
mcc