The issue is with the requirement of a security. Winheller do phrase it carefully as "in their view" a security is not required, but that would have to be agreed with the tax authorities in advance and there are different opinions on how likely this is without a firm legal ruling from the law courts.

(What I find concerning is the attitude of the German tax authorities in their continual attempts to strengthen and increase the scope of this law. They are always trying to broaden it leaving it to individuals and the courts to push back on them.)