The decision has two important implications.
First, a broad definition of arms is actually a very good thing in my humble opinion as it makes it a bit more difficult to argue that the Second Amendment protects some firearms and not others. In order words, the scope of 'arms' is not so narrow but rather more diverse. Of course, that won't stop the semiautomatic gun ban crowd, but it helps a little.
Second, when, SCOTUS finally gets around to holding that the Second Amendment is not limited to one's dwelling (i.e. in public) then this case will gain far more importance for knife rights.
Let's not forget that the case isn't over yet, it could be appealed (which I actually hope it is since I believe the decision would be upheld).