Don't we already have this law in Hawaii?
An excellent point. Here, the law requires you to turn in all firearms if you are subject to a TRO.
I believe the difference in the CA law is that a TRO can be initiated against you simply because you have firearms and someone feels you may be a danger.
In either case, TRO laws are one of the most abused in the system, and also one of the most useless. If the subject doesn't give shit about going to jail for beating the shit out of his girlfriend, or family member, the fact they are also violating a restraining order isn't going to be any kind of deterrent. The record is pretty clear, in fact, a TRO may actually make the situation worse by enraging the potentially violent party.
A piece of paper isn't going to stop someone with violent intent.
Better to be prepared to defend yourself, by whatever means.