they seem to be on every new pro model out there. cwb has those deep single spine down the absoulte n transcend. whereas double spine on the marius. similiarly for LF PS3 and Watson. Both have double concaves according to the specs. They are stated to provide softer landings. which is true if you examine the physics.
Can any give any input which works best? i love the substance i'm on...but my knees aren't agreeing with me.