Gun show pick up

I recently went to a gun show and picked up this crazy piece. It’s a AP M9 from the 80s. It’s all metal and comes with the ability to turn it into a carbine. It comes with the stock, the longer barrel, a mag holder, and extra mags. But the best part about this gun is that it’s factory Glock 19 mag compatible. I checked it and it works just like any other Glock. It was only $300.