Ab wheels are a low-tech piece of equipment that has been around for decades and used by athletes and trainers on a consistent basis.
It is basically a wheel with a rod running through its center; your hands are placed palm side down on each handle. The best ab wheel is a dual one with a wider base to aid in stability.
It is meant to roll while you are using it so that you can move your body forward and backward in different directions, and you will be able to focus on individual muscle groups.
Keep in mind that you are rolling with control–you are the one directing that wheel and making sure it moves back and forth the distance and direction that you want it to go. Later on, you can determine the ab wheel effectiveness.
No matter how long it has been around for or how much people use it there’s always going to be the ones who wonder the ab wheel effectiveness.