All QX series models use the very best high end components. 
If you're looking for the best - this is where to look...
Disc-brakes give you more precision in brake-handling and more consistant braking in different riding conditions (e.g. dry, snow, rain etc).
All QU-AX disc-brake unicycles come with a QX-series rotor (160mm) and Shimano BL-M-445 disc-brake and saddle mounted Shimano BL-M-445 brake lever
The QX-series disc-brake frames have a postmount socket that makes adjustment really easy, no special tools needed and minimal maintainance.
The QX-series disc-brake hub has the standard bearing-to-bearing distance of 100mm. The axle is hollow-drilled which makes it really light.
The new QU-AX 6061 alloy cranks (all disc-brake-unicycles come with 145 mm cranks) are really light (470g/pair), anodized in titanium-grey, ankle-friendly and very stiff.