Yes, they're ok-ish. But the original claim was "MariaDB isn't a replacement for the stock version of MySQL".

Actually yes, it is. It doesn't work the other way around (for example timestamp column has a different description, so dump cannot be loaded into MySQL). But you can use MariaDB in place of MySQL and there should be no performance degradation, since they come from the same codebase.

Reliability was mentioned too - in that case Oracle actually failed by holding back tests. In MariaDB you can reproduce testing if you want. In MySQL not anymore.