There are another spring kit our there which is H&R and it cost a lot less than the KW, but it is not adjustable. The H&R one lowers your f-pace by 30mm while this KW kit lowers by 15-30mm, I have my springs adjusted to 20mm lower than original. Please note this kit is for the dynamic suspension only.
I installed the springs along with 15mm wheel spacers in the front and 20mm in the rear.
I thought the aftermarket springs would be a little bit harder in the first place but I'm wrong. It's a surprisingly comfortable ride. Big difference when going over speed bump. The softer ride doesn't really hurt the handling, perhaps the wheel spacers may helped a bit over here.
After all I'm very happy with this mod. The only downside is cost, it's rather expensive. I spent US$1000 + labour (ordering from Hong Kong) for the spring kit only.