Sony has developed in an inventive, and much cheaper, solution to giving PS4 gamers a key feature from Microsoft's expensive Elite Series 2 controller. The new Sony DualShock Back Button attachment for the DualShock 4 controller adds customizable paddles to the back the device for faster, more responsive gaming.
https://www.notebookcheck.net/Sony-surprises-with-new-Back-Button-OLED-paddle-accessory-for-the-DualShock-4-controller.447871.0.html