That may not work correctly as updating meta-date using the "Fetch meta-data from server" button may update the rating. If you never update the meta-data automatically then that shouldn't be a problem, but otherwise it could cause confusion and missed books.
For me, I've found the best way to handle this is to have a tag called "Read" that I add to those books I've read. That way, I can filter on both Read and not Read books as Calibre allows searches that exclude tags.
Hope this helps.
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