If you’re not concerned about them starting to require that you use Synology-branded hard drives, then :

For most Synology services/apps, we do not collect data on what you store or what you do with your files. We generally only collect statistical data on what packages are installed and which functionality is used. This helps us keep track of what features are important or popular. Purely statistical data is not linked to your account and does not include Personal Identifiable Information (PII). (Source: the other forum)