How effective of a combat technique is a spin attack with a sword that actively propels you? How might it change the development of combat and counter-techniques?
Most experts of real-life combat will tell you that executing a "spin attack" with a melee weapon such as a sword is impractical - it is slow, it leaves your back vulnerable, and it's not nearly as useful as seen in fiction. However, this ignores a common trope that is often being used in fiction: that, through magic or the like, the spinning motion is "powered", turning the fighter and their weapon into a living buzzsaw.
A common example of this is seen in the Zelda series, to varying degrees. The sword will be charged with magical energy that is released, and this propels the user unstoppably 'round and 'round, until they firmly plant their feet and bring themselves to a halt (or, sometimes, spin so much that the energy runs out and leaves them dizzy). It is somewhat akin to the sword having rockets strapped to the blade which adds continuous momentum over the duration of the spin. In essence, the swordfighter is not spinning their sword, but rather, the sword is spinning the swordfighter.
What are the implications of the existence of such a technique? Would it be unbeatably fast and effective in close-combat? How fast could the spin be executed - would swordfighters be more limited by the G-Forces they can sustain, akin to modern fighter pilots, than by any traditional warrior traits? How would historical weapons, armor, and techniques change in the presence of a magically-rocket-powered-spinning technique?