I used the push pins that came with the chin but I also used some self tapping screws at the wheel wells and in the middle for added strength.
Also when installing you have to line up the spoiler at the wheel well if you don't want the gap there. It won't fit flush in front though. It will be set back of the stock bumper slightly...I've bottomed out several times on low curbs and the chin hasn't budged at all.