Velogical rim dynamo vs hub dynamo?

Anybody have experience with a Velogical rim dynamo? I saw two on bikes at PBP and wonder how they compare to a Shimano or SON dynamo hub, especially on bumpy or gravel roads and single track, rain, mud, etc. They are super compact and lightweight and one was on the Alex Singer bike for the Concours de Machines so I figure that says a lot, but I'm curious to hear from people with first hand experience.