The wiki article :
- specifically says that packages are not thoroughly vetted
- does not recommend using yay or another AUR helper (which is the primary thing I recommend against)
- has a frequently asked question section that is fairly technical and should indicate that it is not for the faint of heart
The aur helper wiki has a fun red disclaimer at the top that no one reads
To reiterate, I don’t think there is anything wrong with using the AUR. I think that using an AUR helper that ties updating AUR packages to your pacman -Syu is a trap that people keep falling into despite the warnings in the wiki.