I think people will assume their data is safer with Mastadon. But in a way, your data might even be more insecure, as you have no idea what and who the Instance owner is, and what they will do with the data.

Also, now the responsibility of securing the platform is in the hands of the instance owner, whom you have no idea how they have their platform setup.

FYI, an open source project called Drupal, was recently affected with a a bug where millions of sites could be hacked.

Now I'd like to know how Mastadon will combat these issues.