Sorry, getting further off the original topic, but I think it's an important point. And IANAL so if it's really important to any readers, consult a real attorney.

OBG, I believe that reading the explanation at a site like this explains that the CA DOJ never actually went through the process of making that memo a legal regulation. As it stands now, the law is pretty clear about what is considered a "detachable magazine". The CA DOJ was trying to "clarify" the law in that 2006 memo by requiring that any modifications, like the Bullet Button, had to be "permanent" but the wording of the original law makes no such distinction and the DOJ itself did not require such modifications to be permanent before this 2006 memo.

That memo is just a memo. The CA DOJ tried to submit a new regulation to that effect, but let it die and the time limit to approve that change has expired. So, for now, the Bullet Button, Prince50, etc. are not illegal unless the CA DOJ submits a new resolution to make them illegal and gets that through the regulatory approval process.

Anyway, for anyone interested in learning about how Californians can own "assault weapons," that first link up above is a good summary. The webpage also has a link to the 2006 CA DOJ memo in question.