Maybe i'm a little late to help out here :p
But i'm looking in lowering my car so i contacted a really good suspension installer shop who told me the ST suspensions are practicay like the KW coilovers (they're sister-companies) and that the ST X is the equivalent of the KW V1 & the ST XTA is the equivalent of KW V3
the major difference between ST & KW is that ST is zinc coated where KW is all inox
which also explains the huge difference in price! They are great suspensions kits though, at least that's what they told me! & true not many reviews cause not since long the old weitic changed to ST Suspension
But in
The end it's kinda like this --> ST = great KW build quality & precision but gotta watch out if you live by the sea or in snowy areas
Hope it kinda helped out if anyone still needs (or maybe soon need) the info!
Grte