I've been looking for answers for this for ages, as you can see last comment on the above link was from me
From what ive been reading up, the whiteline kit offers a "mild" setting - where as the Whiteline offers a Soft Mild and hard.. I think first though I will be purchasing the Ultra Racing one - mearly becuase i dont have to take a drill to my little car..
I've also heard complaints that the WL Kit sits really low and causes problems going over bumps, if the Ultra Racing one is like this, then its easier to remove if you needed to!