The Q-Axle disc-brake hub are the successor of the QX disc-braked ISIS hub. The ISIS axle has here been replaced by a technique that has been used in the cycle industry since 2002: The axle has a 24mm diameter instead of the ISIS-typical 22mm and is more hollow which makes it lighter (the bigger diameter allows a thinner wall). The cranks are no longer tightened as much on the axle as possible - but precisely positioned by an alloy cap and then fixed by tightening 2 allen-key-screws on the crank. The crank-connection has less wear and is more resistant to frequent assembly/dissassembly. Also, just like from tapersquare to ISIS, the connection-surface that transfers the pedaling-power is bigger.
Thanks to the more hollow-drilled axle, already the hub is more than 130g lighter than its ISIS-predecessor. It also makes the axle stiffer. As the bearings still keep the same outer-diameter, the hubs are compatible with all ISIS-ready-frames.