The SOS kit (aka TundraRacing.com) was the same kit TRD used to drop some of their early Tundras before they had their own kit. It costs about half as much as the TRD setup, and it doesn't hurt the ride. Read the summary at the end of this article for a discount:
Toyota Tundra Lowering Kit Review | tundraheadquarters.com
As for the setup, you move the rear leafs from above the axle to just below, and as Someone said (good moniker btw), there's a new spring perch on the front coil assembly.