If u see these ab coaster things in a fitness store, online or at a gym where they're more commercial, don't go for it, they're a waste of $ and time. Unless your goal is to work your hip flexor muscles that cross your hip joints & connecting to your vertebrae, you don't need it. You think it's working ur abs but not for very long. Your hip flexor muscles cross your hip joints, the one major group is the (iliopsoas), the iliacus sits on the iliac fossa of the pelvis, and the psoas major attaches to the lumbar vertebrae. The muscle group helps you bring your knees up or sit your whole body up. These are as stupid as doing hip/leg raises on the floor or on knee raise machine that you rest your elbows on.. If u study what the muscle actions are & their attachments, then you'll understand how exercises work. It's Kinetics..
