The standard kit is a ok kit, but its very limited. The upgrade to the SuperFlex allows more preset adjustment and axle flex. By added adjustable track bars front and rear: you can center the axles properly. Also adding a set of adjustable control arms, the front caster angle and rear pinion angles can be adjusted. On my suspension, I opted for the 4.5 SF kit with upgrades for adjustable track bars and control arms, and subsutited the springs to 3.5"
I've installed a number of these lifts and I can tell you its well worth the upgrade if you can afford the extra $$.
[FONT=Trebuchet MS]01' Jeep TJ (Jeep #5)
3.5 RE Custom SuperFlex, Raingler, Kilby, Currie, Banks, Borla, American Racing, Custom mods, Always more in the works.