Hi,
The early speedo [black plastic] used on the 99 model doesn't do well. I have thrown away about 20 of them. They are plastic and the insides fall apart due to the motor vibration. The needle falls off on many of them. Most stopped working in less than 500 miles.
Sadly I still have several in stock, but am to ashamed to sell them to anyone. When Whizzer offered them to me as a close out special, I took a pass. You would be much better off to purchase a "vintage" bicycle speedometer on Ebay as at least they will hold up much better.
The later versions are much better and are made from metal, not plastic. Of course the "good" ones are hard to find. There were 2 versions of the metal cased speedometer, one had a black face and the other has a white face. Both metal versions hold up well.
The metal versions are very accurate, whereas the plastic version is very optimistic [off by at least 15%].
If you don't care if they work and only care about "looks" then the $30.00 price is good. You can use the original new edition Whizzer cable and wheel drive or find the drive unit from a Schwinn 26" speedometer [same ratio].
Have fun,