Operates yes, but design I believe is where the legalities start. I'm making an educated guess here. I'm not entirely sure how the whole patent thing works. but if it at all resembles copyright law then you can have a mouse character, it just can't look exactly like Mikey Mouse.
Example: Plinker and NDZ both make an after market 15-22 charging handle, however if you look at them side by side they are designed differently. It might be miniscule but they are different. Do the Pro-Mags and Plinker Mag's look exactly like a S&W mag? No. I'm going to wager that with submitted designs, he can have a magazine follower that functions the same as the others, it just can't be designed the same way if there is a patent on that particular piece.
Or he is just trying to design it different for the sake of being different and it's not working out as planned.
People were always pushing me to file for a patent with the dust covers I made for the 15-22, but I always sort of figured, it's been invented already, it's not new and unusual.
I'm sure I'm not completely accurate here, someone please correct me if I'm giving bad info here. I just tend to look at it with the understanding that if it's proprietary, then it's protected.