[leftybass209]

Bags are great for passenger ride comfort and for the aesthetics of laying a truck out. For the performance oriented driver, the streetgrip system you are interested in would be better. Springs will always be springs though. A change in spring rates will adjust firmness or softness but ultimately you'd never get:

bag comfort from springs, or spring performance from bags. (when comparing the best setups of both)

That's not to say there aren't performance rides that use bags, or plush comfort rides that use springs though.

That streetgrip setup is just using dual-rate (variable rate) springs which changes the spring rate character as weight is applied to the truck or during hard-turning/acceleration.

Any quality variable rate spring and a good adjustable shock would perform similarly. They're just using delrin bushings as well. It's not a reinvention of the wheel, but rather a package that encompasses some performance oriented parts in one kit.