Thomas, as Ronny pointed out, SuperFields uses SLF4J, so any rules related to configuring it should work.
But I agree that some of those log messages are too detailed and should not be by default logged. Plus, the docs could explain how to configure logging. So I made a ticket https://github.com/vaadin-miki/super-fields/issues/292 and I will have it done by the next release - I hope this makes the add-on more user-friendly. :)