The H has an update on this: ( www.h-online.com/open/news/item/AVM-cannot-prohibit-modification-of-GPL-router-firmware-1377041.html )
"In its decision, the court rejected the claim by AVM to ban the sale of Cybits software. Both Cybits and other third parties are allowed to make changes to the Fritzbox firmware. Cybits is also not prohibited from selling software which helps the user make those modifications. However, the court did rule in AVM's favour to enjoin Cybit from distributing software which made the router display incorrect or faulty status information. AVM claimed that the use of Cybits software made it appear to the user as if the router had malfunctioned."