A powertrax noslip has been on my wishlist for quite a while. I would think it would be comparable to qdii to the point of indistinguishable. Main difference is mechanical vs electronic and true locking vs clutchpacks. I would think there would be less to go wrong and easier to fix.

Only thing missing is a front locker, but with the break traction control i doubt you'll miss it. I also doubt qdii engages the front lsd/locker often in real use.