The installer installs the binary to /usr/local/bin, which is system-wide, but the launch agent to ~/Library/LaunchAgents, which is user local. This sort of inconsistency is not desirable, and it should probably install the launch agent to /Library/LaunchAgents.
In particular, this is problematic because I use brewdo, which means I get permissions errors on installation when the installer tries to write to ~/Library/LaunchAgents.
See also my post on Homebrew Discourse.