The ECHO Sport is an economical pull and release trigger for the AR-15 platform. The ECHO Sport has the functionality of the ECHO AR-II. Echo Mode: Firearm fires when trigger is pulled and also when trigger is released. The only difference is that you select the ECHO mode from the paddle rather than the safety selector. You can negate the second round but you do it off the paddle, rather than the safety selector. The ECHO Sport gives you all the functionality with a more affordable price.