Sorry I don't have experience of them, but if I wanted coilovers I'd buy the Gaz ones.
They have zinc plated threads and powder coated bodies plus IIRC the steering arms are lowered. I'm pretty sure you can specify the spring rates/lengths when ordering too. Topping it all off is the fact that the dampers are adjustable and have a 3 year warranty - win win as far as I can see.
Can the KW or H&R kits perform or really be that much better, paticularly when cost is taken into consideration? Rally Design currently list the Gaz kit @ £475 + VAT. I know where I'd spend my hard earned.
Hope this helps.
Richard.