As a general rule, multiple shock systems will distribute the workload over two or three shocks - depending on if you get a dual shock or triple shock set up. For smaller trucks and SUV's a dual shock kit is plenty. Even on a full size truck a Dual shock kit will handle most jobs. However, if you are into aggressive off-road driving, or you plow snow on a regular basis, a triple shock kit will give you optimum performance and durability.
Most of the multiple shock kits listed do not include shocks - you must purchase them seperately.