App effectiveness

Just curious here. Does anyone happen to know how effective this app is on preventing pregnancy? I use it to track my periods and predict my ovulation. Does anyone know how helpful this app would be at helping me prevent pregnancy also. (I'm also on birth control but I don't have that in the app because I like the think of that as more of a "safety net" but I've also heard of horror stories.) Any advice would be greatly appreciated. Thanks!!