I've had the good fortune to possess two Holley Magnetos, a 1906 and 1907 version. There was also a 1908 version, and each was standard equipment on the three year Model K Ford.
The concept the first Huff magneto began with Nikola Tesla. From Wikipedia:
"Most ignition systems used in cars are inductive discharge ignition (IDI) systems, which are solely relying on the electric inductance at the coil to produce high-voltage electricity to the spark plugs as the magnetic field collapses when the current to the primary coil winding is disconnected (disruptive discharge). In a CDI system, a charging circuit charges a high voltage capacitor, and at the instant of ignition, usually determined by a crank position sensor, the system stops charging the capacitor, allowing the capacitor to discharge its output to the ignition coil before reaching the spark plug."
As with the Model T magneto, Ed Huff was inventor of what became the first working CDI system in the world. While Tesla patented the theory, no one developed the switching system to use the magneto before Huff. As with the later T mag, Huff applied for the patent, but it was also assigned to Henry Ford on the patent application. The patent was applied for in the summer of 1905. The magneto was already in use on the Ford six cylinder racer, first seen by the public in January 1905.
The first variation of the magneto had no advancing system, and this was changed in the 1907 and 08 versions.
Below is a photo captured from the video link below it, showing the spark, across about 3/4th of an inch at 300 rpm. The spark is so hot it will jump up to 3 inches at higher rpm, and I am able to crank start the Model K on magneto with this unit.
Link showing Bruce V. S. running the mag with a drill at 270 rpm. The magneto is putting out about 300 volts at this rpm:
https://www.dropbox.com/s/1bx3ad41cojqp ... g.mp4?dl=0
Henry Ford and George Holley collaborated to produce the magneto, and in addition to all Model K, it was standard equipment on Grout automobiles. Other car makers, including the Thomas Forty offered the Holley magneto as optional equipment. Below is a letter from George Holley to Henry Ford dated Dec 14th, 1905. Holley describes his efforts to market the magneto to other car makers, as well as comparisons with other makes of mag:
Below is a photo of Frank Kulick, Fords race car driver, seated on the 1907 six cylinder racer. Just forward of his right foot one can see the distributor head and magneto body, mounted vertically on the racer. This is same magneto used to lead Ford Model K to several racing and hill climb victories, including the world 24 hour speed record set in June, 1907.
If you watch the video, you can see how incredibly hot the spark is. The effectiveness of the magneto is also it's biggest downside. It's so hot when any moisture or insulation weakness occurs, the magneto "burns itself up." Bruce just rebuilt mine for a second time, and we're ready to use the mag again.
One unique feature of this magneto is that it will work when the magneto portion of the device fails. There is a two way ignition switch, and you can switch the mag on, off, or to battery. On battery, the magneto acts as a distributor and master coil system, using one coil and capacitor to distribute the spark, much the same way a modern distributor does.
I think the other downside of this magneto was it's expense. As George Holley mentioned in his letter to Henry Ford, there were too many parts and it was expensive to make.
Mike Kosser reviewed the wiring diagrams of the mag several years ago, and pointed out that this is a capacitive discharge ignition system. As far as I can tell, no production automobile offered a CDI as standard equipment again until the late 1950's.