That was a very biased reaction by the person that posted the differences. In fact the differences he posted had nothing to do with how the rode and everything to do with the supposed durability in an area that does salt its roads. Thing is even though he says he did not drive the car in the winter Salt does not easily wash away and once you do get some on/in your car its extremely hard to get rid of.
In fact its so hard that cars that run Bonneville Salt flats actually get dissembled completely and gone over excessively after each time out on the flats.
I am not trying to start controversy here just stating that while the person had a problem its one of hundreds of thousands that run ST springs and coilovers with no problems . You never here from the happy people you only here from the people with problems.
That was/is me. My reaction wasn't biased at all; I have no skin in the game not having any interest in either ST/KW or YCW. My experience is pretty easily explained: I own a set of ST XTA's, the springs corroded enough during 3 years and ~ 7500 miles that one failed and the others appeared to be close to failing (I posted the pictured), attempted to make a warranty claim only to be lied to and ignored by ST/KW, and took them off my car and replaced them with YCW's with Swift springs.
The coilover hardware included with the XTA's is far inferior to that of any other set of coilovers that I've owned, including the YCW's: plastic threaded perches, a set screw instead of a locking ring, lots of grit and grime traps in the spring stack. The dampeners seem to be fine except, again, grit and grime traps. The coating on the dampeners is thin and did not weather well. The YWCs have a nice, evenly coat of something tough, come with traditional coilover hardware (metal perches and locking ring, clean spring stack), and the height adjustment is separate from the spring pre-load, as I'm accustomed. Swift springs are top notch.
I didn't compare the ride or handling to avoid an apples/oranges comparison; the ST XTA's are sprung for the street and have progressive springs (in the back) and I specifically ordered racey linear springs with the YCW's. I will say, after having the YCW/Swift setup for some time, I much prefer the ride and handling of a linear setup.
If you drive someplace *that never salts*, the ST/KW springs might be fine, although they are cheaply built and poorly priced given the alternatives. If not, don't buy them. I never drove my FiST in salted conditions and usually unwrapped it pretty late into the spring. Even so, the residual salt on the road rusted though the springs that ST/KW uses on th XT, the XTA and the KW variants. The springs are sub-par.