Installation takes a couple minutes to figure out, besides that it feels really nice - FAB Defense AR15/M4 Collapsible Buttstock for Mossberg 500 w/ Shock Absorber Option

Besides there being no instructions it feels really good in the hands once it is installed. Installed it onto a 590a1. Here are some simplified instructions to save future people a little time since there are no videos out there on it. Open the pistol grip itself, take out the bolt needed to put the grip on the gun. Fold the stock to allow access to bolt holding grip and stock together. Take out the bolt and take off the stock, leaving just the grip. There should have been a cap with 2 prongs that came with the order, use it to remove the metal cap that is used to connect the grip to the rest of the stock (there will be 4 or 6 indents in it). Once the metal cap is out you can use the bolt that came in the grip and install the grip onto the gun itself. Put the metal cap with the indents back onto the pistol grip, put the stock on top of the pistol grip and then screw in bolt that holds together the pistol grip and the stock. Done.