I didn’t even know about libredirect :)

Just so that you have an additional data point, here’s how I do it.

I run a backup first, using borg-backup. I used rsync in the past, then rsnapshot and now borg since it allows for compressed incremental backups, diffing on the “chunk” level, meaning I won’t backup the entirety of a modified file again and safe a lot of space.

I used yay before, but like you I didn’t want to go into it blindly and do some modicum of sanity-checking the PKGBUILD for changes beforehand. Since it wasn’t obvious on what would be the best way of using yay for doing this, I asked around on the ArchLinux Forum, and ultimately decided to try one of the simpler tools suggested in the Arch Wiki, aurutils.

After setting it up (the author helped me migrate), I now use it as follows:

• aur repo --upgrades: Searches for new versions of aur packages and displays them
• aur sync --upgrades --no-build: Performs a git-pull under ~/.cache/aurutils/sync and opens vifm so that I can look at a diff of the PKGBUILD and all the other changes in the affected directory.
• aur sync --upgrades --no-view: Builds the package. It is now available as part of the custom (local) repository used only for aur packages, but hasn’t been upgraded yet. That is, a package.tar.gz or whatever has been created and put into ~/.cache/aurutils/sync/, where the PKGBUILD resides as well
• sudo pacman -Syu: Upgrades all packages from all repositories, including the ones from the custom repository

I won’t argue pro or against one aur helper or the other, but I feel like I have a little more insight about what happens under the hood since I made the switch. That being said, in the very beginning, I managed aur packages manually. This works also, but at some point became too tedious for my taste. I am happy with the semi-automatic approach I am using now.