In California, owning an "assault rifle" is illegal. An assault rifle is defined with some specific definitions...not limited to, but we will use in this example pertaining to the magazine:

A semiautomatic rifle that is able to accept magazines AND have blah blah blah features. With the lock kit, the rifle is NOT able to accept magazines, since the magazine is locked onto the rifle and can NOT be removed without the use of a tool...therefore it is NOT an assault rifle. Once you remove the lock, it will be able to accept a magazine...and if it has blah blah features...it is now an assault rifle.