Yeah the wheel on mine had a bad spot, BUT you can turn the wheel around and sometimes that takes care of the problem. I had to true mine up on the lathe, but cutting a little bit off doesn't affect the rpm tach or any functions. The dizzy is just a early 70s motorcraft one for 289/302, I use it to run engines on my test stand.
These machines work by simulating an ignition system (for lack time giving a more in depth answer) and instead of firing an ignition coil you are flashing a light, much like a timing light. On a 8cyl engine you will have 8 arrows around the degree wheel, a 6cyl will have 6 arrows, one for each time the distributor sends a signal to fire the coil. This allows you to visually see when the coil fires, and it also allows you to see how much mechanical or vacuum advance the distributor has, and at what rpm it starts to advance the timing. In the video the distributor has 15 deg mechanical advance, I also checked the vac advance (not on the video) and that is also 15 degrees. These machines makes it easy to change weights, springs, and other internal components in the distributor and then check to see what affect it had on how fast or slow the mechanical or vacuum advance come in, and how much advance is added or removed.
The goal is to adjust the ignition curve ( amount, and rate of mechanical/vacuum advance) to what an engine likes, in order properly fine tune an engine. Most people just plop in a distributor and are mostly concerned with total timing, a properly curved distributor will make tuning a whole lot easier, and the engine will be snappier (is that a word?).
