Radial side cut mean your side cut follows a constant radius which was the standard for many years, mervin then adds extra contact points with the magnitraction bumps. I feel mag really shines on icy traverses, expecially one foot traverses, and puckered ou situations in steep terrain. Some feel it has too much grip and can be hooky. The only times it doesn't fell smooth is sliding perpendicular to the side cut on firm snow. Vario grip uses sections of different radius starting tight at the tip and tail, then a medium section, then a mellow section in the middle. When you ride magnitraction in soft conditions it feels as if it is a smooth radial side cut. On firm snow you feel the extra grip but turns still follow that constant radius. Vario grip does give a good edge hold but with other variable/progressive side cuts you can the arc of the turn change as you come through a turn and your weight shifts. Angrysnowboarder.com has a good write up on sice cuts.