Could you maybe elaborate on your statement that...
> Gentoo overlays are better designed than debian/ubuntu PPA(personal package archive)s and AUR(arch user repository).
...because from what the Gentoo wiki states, an overlay is a repository of packages from which Portage will automatically install packages. That is a clear contrast to the AUR from which you manually get a package so you have the chance to inspect it without Pacman automatically going and installing it. For Arch a closer equivalent would be unofficial user repositories.
> Gentoo overlays are better designed than debian/ubuntu PPA(personal package archive)s and AUR(arch user repository).
...because from what the Gentoo wiki states, an overlay is a repository of packages from which Portage will automatically install packages. That is a clear contrast to the AUR from which you manually get a package so you have the chance to inspect it without Pacman automatically going and installing it. For Arch a closer equivalent would be unofficial user repositories.