mp3tag will Save before it Removes. That is, when it sees ID3v1 it will read that, copy it to ID3v2.3, then removes what you don’t need.
And the Extended Tags thing is essential. A lot of rippers have the bad habit of putting the album cover inside every file as imbedded art.That is a huge slowdown. Highlight them all and if Extended Tags shows the album cover, it’s in every file. Click on the floppy-disc icon, which will extract and save one copy of the art as folder.jpg (or .png or whatever format the art was). Then click on the X (lower right) to get the art out of the tags.
