Several of the implementation flaws allow an attacker to essentially inject plaintext frames in a Wi-Fi network. All that's needed is being within range of the network (with an extender you can still be far away). I agree that the design flaws aren't that serious! But that's also explicitly mentioned on the website so...

Edit: injection can be used to punch a hole in the router's NAT so someone can directly try to attack your devices. As always there world isn't burning down. But I think it's interesting research :)