I just ordered a set of Super Springs from JC Whitney (they had free shipping plus a 10% off coupon.) I have various methods of hauling my dirt-bike in my truck, I can either load it straight into the bed or onto a hitch carrier (like this one: 400 lb. Receiver-Mount Motorcycle Carrier). Generally when it's just me I prefer to use the hitch carrier since it's way simpler to load and unload by myself. The unfortunate side-effect is that it puts a ton of weight on the back of the truck since it is effectively using the rear wheels as a fulcrum on a longer lever than normal. I'm hoping these springs help keep the sag out of the back of the truck since right now it looks like I have half a low-rider.

There's another style of overload spring but it doesn't ride over the top of the axle, it uses another set of U-bolts to mount on the existing leaf spring down near the axle itself. I prefer the simplicity of the Super Spring and I am very sure that mounting them will be faster as well (I also think having one solid stick of metal rather than two pieces will be more reliable in the long term.)