Honest question: how's that different from running Software Update from the 10.15.3 install to get to 10.15.7? (Other than working offline once you have the update downloaded, that is.)
It's also good to not need to connect to the App Store, with all the 2FA involved. That would associate my Apple account with that computer, and save my password in the keychain. (Yes, I know I can delete it, but I want to leave the migration running overnight and just tell the user to reboot when it's done).
My biggest pain point was that the downloader portion of the updater is so low quality. It corrupts downloads or restarts with tiny network blips, can't resume most of the time and often much slower to download than available bandwidth (that might a bad routing issue on my country). Overall it's often a painful experience.