the original on the Ducati is a single induction sensor, which gives a sinusoida wave form. thats OK for most instances but it does have disadvantages... firstly you need a fairly large diameter wheel (like a flywheel) to sense off. then you need to calculate at what point on the slope on the wave form the sensor picks up the signal... again that's OK as you can enter a compensation factor in the ignition software, however the point on the curve that it triggers is not linear in that it moves along the curve as revs increase.
the hall effect sensors have some distinct advantages. firstly they work off a square wave form, so it's essentially on or off with a precise cut off point that does not change with RPM. they can also be used on small diameter wheels, Like a cam wheel in this instance as they are not reliant on a chunk of steel passing in close proximity like the induction ones. They are also physically small. Most cars and bikes use Hall sensors these days for things like crankshaft and camshaft position sensors. they are also cheap... these we £1 each!
using the hall sensor also allowed me to get rid of the wasted spark as I can configure the software to spark every second revolution