And when that plastic mag breaks a few years from now, the next one, if you can find it, will cost $325. Also, how many pistol mags of any kind made before 1950 are still reliable enough to stake your life on? None that I know of. Weak springs and bent followers can be replaced, but if the housing, which is the part regulated by the law and can't be replaced, gets banged up it's usually never completely reliable again even after it's repaired.
Keep in mind that if another AW ban is enacted it probably won't have a sunset clause. That means your grandkids and their grandkids will never be free from these restrictions even if no other gun laws are ever passed, which we all know isn't gonna be the case.
Now, is that enough reason to write your congressman?