Every module that is part of the core Moodle has gone through a thorough quality assurance process. The potential problem with third-party add-ons is that you don't know anything about the quality of the software.
While it is possible to uninstall modules if they don't fit the purpose, you will have to make sure that you don't put barriers in place for future updates. If an add-on is not maintained, it is unlikely to support any forthcoming versions of Moodle and you will have to delete the module already in use or you won't be able to upgrade your system.
There are a number of criteria that indicate whether an add-on is trustworthy or not.
Moodle keeps statistics about downloads from Moodle, which you can find at
download.moodle.org/stats.php. At the bottom of the page you will see a table listing the top 50 plug-ins downloaded in the last 60 days. While this is no guarantee, the more popular a module, the more likely it is to be of a high standard...