Using AMD's installer is stupid, they mutilate your system, and "when it breaks,you get to keep both pieces". Don't use them. (At least not directly) The buildpkg option might build a distribution package for you which installs in a well-behaved manner, but just using the script and installing it from that is a good way to wreck your system. It's not a matter of, but when. Even if it appears to work at first, an X server or kernel update will come along and break it. (This is another issue, separate from overwriting core system files.
Same advice typically applies to Nvidia, don't use their installer.
i don't use the catalyst installer i use the ubuntu/kubuntu package based installer.