ok, here's a start on explaining what it looked like:
Now, this thing here isn't nearly as good. The base has to be filled with sand or water -- the last things you want on a tennis court. The Contraption, in contrast, is stable because of its wide base.
This thing has a foam ball attached. The Contraption had a regular tennis ball with a steel dowel running through it, so it spun freely and had the feel of a regular tennis ball. I assume the tennis ball can be swapped out when it gets old.
I'll keep looking, but I doubt I can find a picture of it. He said he bought it in Florida.