I presume you refer to http://www.silentmaxx.de/
The company has been around for a while, nearly a decade. Used to offer fanless PSUs -- not very reliable, at least the first ones, but probably improved as suppliers got better. ( like this -- http://www.silentpcreview.com/article312-page1.html
If they're using good components in a well ventilated case or direct heat conduction to the case (using heatpipes), then the systems should be fine. But I'd opt for lower power components in a fanless build. Less heat, less potential for trouble.