most people do not use this setup for one or more of several reasons. 1 they have never seen it, so they don't know it exist. 2 they may not like their car as stiff in the front as I do. 3 They may be afraid to make homemade or non engineered mods to their car. all my modifications are preformed by Accidental Engineering Inc.
As far as How the leaf spring works ... The transverse leaf, is actually the longest leaf from the rear of a 1200. The ends have been cut off, a 1/2 hole centered near each end is drilled, to allow for a 1/2 bolt , also you have to drill 1/2 holes in your lower control arms. Flip the leaf upside down, and use bushings on the ends and for the center a block of polly..... plastic,which is held in place by the spring pressing it against the crossmember. The longer the block the more resistance to bend the spring BACKWARDS. The longer the block, the shorter each end of the spring becomes, and therefor stiffer. When the front of the car, (one side in hard turns, and both sides when breaking) wants to dip, the added resistance of this spring adds greatly in reducing front dip, and therefor also reducing rear tire lift which is undesirable when autocrossing.