In the process of training, you'll acquire greater core strength, stability and muscle coordination than with any other exercise known to man. (fitnessandpower.com)
If you want to develop great core strength AND / OR a flat stomach, this is an exercise that belongs in your program. (hardgainermusclebuilding.com)
This is a difficult exercise that requires a high level of shoulder and arm strength to sustain the hold and strong abs to keep the legs parallel to the ground, but it's incredible at building greater core strength. (fitnessandpower.com)