They even have their own page for the series where you can watch all episodes. Other series can often either only be watched on TV with advertisements or if you pay for them like on Netflix. Is there a reason they did what is known?
I only found the site by chance and wanted to ask whether there's something similar to other series that have their own site where you can watch everything for free and legally?
I can't help exactly, but if pages on which you can see something like this for free end in .de, the probability is high that it is legal and if they end in egto or .sx (i.e. From countries with a different jurisdiction and mostly outside the EU) they are actually always illegal, since there's no reason not to use a "normal" domain for legal sites.
Maybe this rough rule will help you.