basically....

Basic = ride height adjustable, no damper adjustment
SS = ride height adjustable, 16 way damper adjustment
Tein flex = as above, but with EDFC compatability and few extra things that i can't remember atm.

The flex is a flagship basically, the SS is for ppl that need or want to adjust dampening to their personal taste.. basic is for ppl like me that just want to be able to choose their ride height and have an overall stiffer suspension...