They are a good lightweight tough as nails hub that you can pound off-road. They aren't particularly delicate considering that they are made for demanding conditions. There are some of problems with them, however. First, finding a 36 hole XTR hub isn't impossible but it's not as common as a 32 hole hub. Second, if you buy new ones, you'll only find them in disc versions. If you need a disc hub that's good news but if you don't need discs, why pay for the privilege of using them?

Third, they aren't cheap. You could buy a good set of White Industry hubs that aren't disc compatible and run very, very, very smooth on seal cassette bearings for about the same price or you could buy a set of Phil Wood hubs that also run very smooth and can be taken apart with a 5 mm allen wrench for a bit more money. My rear Phil's cassette mechanism comes completely out of the body making spoke replacement on the drive side much easier and simpler.