A magneto is little more than a distributor with a built-in DC generator to provide the primary current & a built-in coil to make a completely self contained ignition unit.

As the RPM rises, the voltage needed to jump the plug gap becomes greater. The voltage output from the DC generator also becomes greater & this increased primary voltage makes for more voltage in the coil.

Modern electronic ignitions can match this performance without difficulty which means that the magneto has a very limited application these days.
Ideal for vehicles that do not have a battery & this would include race cars that are normally push started [speedway, salt lake] or some industrial applications.