I would imagine the build quality to be to the utmost highest standard.
While I haven't used WP suspension on my bicycles I have used them on road and off back home in Australia. I had a set of forks on my main enduro race machine and for my R1100RS back in 1999 I had a custom set of shocks, front and rear, built for the R1100 and to match my weight. Beautiful engineering and the most controlled ride I ever had. All measurements and weights etc were done by fax, built in Holland and then shipped out. Perfect straight out the box. They weren't cheap that's for sure, but worth it.
Jamie