I had an original Xen which was ace but it reached the end of its life when i used it as a face brake :0( was a great helmet tho, if a bit hot, not so much due to lack of vents (there are quite a few) but more the larger area of pads in contact with your head.
Ive just bought a new Xen and having a few problems, the peak on these new ones rattles compared to the old one, the straps dont seem to sit as well (could be cos they are new) and the worst bit is with the new Rocloc4 adjusters, they just dont seem to allow you to tighten it when it on your head or falls apart. Still comfy tho, one of the best helmets i had.