No a move is not safer, the filesystem and the metadata.db database have to be kept in sync. That cannot be guaranteed with a move.
And calibre does not do a copy, it does a hardlink, then updates metadata.db and then a delete. That way the worst that can happen is you have extra files in your library, but metadata.db and the files can never be out of sync.
The only situation where calibre does a copy if is hardlinking fails because whatever filesystem you have your calibre library on is poorly implemented.
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