No one has mentioned the service and reliability issues of CK rear hubs. Yes they are lovely but I could never get mine to stay tight. I was running it on a DH bike, but the cones were forever coming loose, like literally every five runs or so.
Also, you do need to service them pretty regularly and it's only possible to do it properly with the right tools, which cost over £100. I was servicing mine every 6 months because of what I was doing on it; perhaps for trail use they wouldn't need that much attention.
The alloy cassette shell can get chewed up, especially if the owner has been running a road cassette where the sprockets are separate rather than on an allow carrier
They are lovely though.