The KW kit is very good, I've had it on for a few months now. The main differences I have noticed are slightly more rebound than standard so you notice a slight bouncing down the road feel on bumps and MUCH better road holding, the car feels much more planted on high speed sweeping bends and gives alot more confidence that its not going arse out any second.
The height is good as I don't really hit speed bumps anymore than I used to. Had four people and luggage in the car on the way to the V festival last weekend and the rear wheels were well into the arches, don't think I'd want to go any lower.