First a question then I will give my best answer on the point of the button in question.

So if this product did allow people to bypass the magazine detachable from outside the pistol grip what firearms would be allowed now that are not currently allowed? THe ruger 10/22 charger pistol is the only one that comes to mind but I have to admit I am no firearms expert. What other firearms would be allowed?


Here is my answer from someone in the LEO field.
I do not think this button would allow one to bypass the 1st section considering magazines outside of the pistol grip. After all the first rule does not say anything about detachable. Now if we look at the initial definition that says the rules apply to a semi auto with a detachable magazine we can see that if we make the magazine non detachable then we never run into the problem of it being a possible assault pistol.

So the question comes down to whether the button makes the magazine non detachable. I would say that the magazine would still be considered detachable since it is relatively easy to remove the magazine.  Now the law is not explicit so this is kind of a gray area. So I think we would need to look at the intent of the legislature when the law was passed. I don't know the actual discussion on the issue so I will do my best to speculate. They probably wanted to restrict firearms that had some significant capability of shooting people rapidly, essential a pistol meant to assault someone, civilian or police. So if a product like this made you need a "tool" to remove the magazine but it could still be done rapidly then I do not think they would consider it to be allowed. However if the product made the magazine take some time and effort to remove the magazine to the point that the pistol would not be such a danger if used to shoot large numbers of people then perhaps they would consider it to be allowed.
If we look at blackpowder pistols we can see they do not need to be registered. They can still be deadly but the amount of time needed to reload and shoot again in a tactical situation make them obviously a poor choice in a gunfight.

So ultimately I would think that if the product requires a "tool" to detach the magazine but the magazine could still be detached rapidly and replaced rapidly that the firearm would not be exempt from the assault pistol rules.

Feel free to disagree or ask for clarification etc.