We don’t need a FAK at all until we do; unfortunately, at that point we don’t get to pick the injury, it picks us. So the FAK’s we carry are hopefully appropriate. If a CPR mask is appropriate then carry it. If you are with a younger athletic crowd and the most likely injury is broken bones or sprains, and heart issues are decades away, why carry a CPR mask. Like M_a_x said — priorities. BTW, I heard the same thing regarding chest compression versus rescue breathing. As I understand, the chest compressions move enough air in and out of the lungs that breathing isn’t really required — focus on the compressions to keep blood moving to the brain. (Which means the CPR mask may be wasting space in your kit.)

The Wilderness First Aid course I took had very little (zero) training on CPR. It was about bleeding and other traumatic injuries such as falls, sprains and broken bones. We improvised splints from magazines and sticks combined with available wraps. We used sweaters from people in the class for neck braces.