The "signal" to fire the coil is when the points OPEN.
The ignition coil is nothing more than a transformer when you get right down to it. When the points are closed, the primary winding is energized and creates a magnetic field. When the points open, the current through the primary winding stops, the magnetic field in the coil collapses and induces a charge in the secondary winding. Because the secondary winding has more wraps of wire than the primary winding, the voltage in the secondary is higher. This is effectively the spark.
Our engines require 2 separate ignition systems because of the 180 degree crank. The coil mentioned above appears to have + (battery) and - (points) stud connections for the primary winding, and 2 connections for the plug wires that will both fire simultaneously.
As Chris has stated, this would work for a 360 degree twin like the XS650, or a single with 2 spark plugs. I can't see how it would work for both cylinders of our bikes. I expect that only 1 cylinder will fire correctly and the other, well... It could get ugly with rough running, backfiring and flames.