In my opinion the plesk composer utility needs some of the functionality that the laravel composer tool has:

1. Ability to run composer commands from the GUI rather than the CLI like the Laravel tool has implemented - if the site/subscription is not a laravel application, you don't have this option. You must use the CLI.

2. Ability to require private repositories - much like the git utility does for cloning a repository. Currently we have to manually edit the composer.json file then either add the users default key to github as a deploy key or generate individual keys for each repository if multiple private repos are needed (github does not support using the same deploy key over multiple repositories)

on the flip side, the Laravel tool could use the same functionality to include private repositories and also a manual editor for the composer.json - again if you have Laravel toolkit installed and no composer extension ... you can't edit the composer.json from the GUI.