I was interested in Piwik until I noticed the many, many open security issues:

https://github.com/piwik/piwik/issues?q=is%3Aopen+is%3Aissue...

Includes an issue from January about insecure random-number-generation: https://github.com/piwik/piwik/issues/9473

and one from March claiming that it doesn't reliably use TLS to update plugins: https://github.com/piwik/piwik/issues/7582

It bothers me a lot when people advocate self-hosted services with really bad security posture to increase privacy (or "control", as the author says).