I have them and am yet to have any major issues. Just make sure you keep the true up on them, especially during the wear in period. I've done a bunch of races incl rotorua EWS and a bunch of shuttling on DH style tracks and they're fine. Only thing that has hurt them so far is me running into a tree.
Edit: Also re the axle unscrewing itself, mine has done the same alot. Cleaning it all out seems to have helped but I've also gone the extra security of positioning it parallel to the lower rear chainstay and putting a few loops of electrical tape around the two.