Since Gmail supports imap and pop3, one could simply use any proven email client to backup the emails. I don't think a special tool that or may not work is needed for this.
gmvault is purpose-built and quite simple. I've used it before with success. It backs up your whole mailbox in one command. Why should we fiddle with a desktop mail client?
How about clawsmail ? It's a pretty good client too, and still updated.