I noticed that too. A lot of German media started doing this ("pur" subscription vs "full" subscription which also gives access to additional paywalled articles). I would be surprised if these huge publishers didn't do their legal legwork - or they are doing it just waiting for a test lawsuit to clarify the reading of the law.
the freemium in itself is certainly legal. In the case of spiegel though it's really accepting tracking for the free articles. sz.de e.g. has the usual toggle option for the different cookies.