There was one from 1973 that I remember, it used analog swing needle gauges for speed and cadence. I forget the name, it started with a W I think. Other than the few that were out there at the time, (it was really expensive) I saw one on ebay over the years, sold for over $400. There was some controversy at the 1974 National championships where Skarin had one on his bike for the individual Pursuit, they let him ride with it but there was quite a debate if he should be allowed to. It was if memory serves, about 3" x 5" x 1.25", not petite, wires to the hall effect sensors.
I wanted one, but the price was out of my league.