So I ordered a monitor which shows how much the unit retards using yellow lights (OK, LEDs). I hooked this one up myself. I rerouted some other wires installed before so that all went through the same hole in the fire wall, making things a bit neater.
The only slight problem was that the instructions described the oxygen sensor wiring for pre-1996 cars. I called J & S, got John (the J), and we figured out that the additional wire was a ground to be ignored.
Good support, but John hemmed and hawed on my questions to be more specific on what is "highway speed", although he agreed it was 65 mph. My impression was that you need to drive significantly faster, but that he did not want to say so. We agreed that the best was to listen for knock (which should not be easy to miss) and adjust the unit as needed. I set the unit to show some retardation during a highway cruise at about 90 mph. (Do not do this at home.)
This sensor seems a better idea to me than a passive MSD device, since it will correct more if you are driving in hot weather (Tallahassee) or if your gas just does not quite make it (California, Texas). I plan to spend some time in California next year, so I will be able to test this then.
The monitor is a conversation piece. Below the yellow timing display is a second display of LEDs ranging from green to red. This display shows the air to fuel ratio (really the exhaust oxygen sensor output, I think.) It will continuously range from green to red. I do not know how important this is, but it sure does make an interesting display.