The ab wheel is a great piece of equipment for hitting the lower and upper ab girdle at the same time. The body can adjust to it pretty fast and 20/30 reps or more can become easy. Standing improves the movement quite a bit, as suggested. Rather than a smooth surface, try it on a heavy rug, gym mat or a natural surface like dirt. Or even a light layer of sand, if your extremely macho. Much more demanding. Also have the feet on a high table or the upper level of an incline bench, on whatever surface you choose.
The ab wheel is akin to a face down straight arm pullover, so the lat's come into play strongly as do the triceps. Actually the ab's keep stable the core section of the mid body during the ab wheel exercise. That's where most of their work comes into play. For a $4.95 investment, it can hold it's own against most $1,000. ab machines. Gooc luck.