I actually met the SpaceBall people several years ago in New York at the "M3" lan party. This was back when KillCreek was among the endorsers, and she was still seeing one of the guys from Ritual, before she hooked up with John Romero and got the boob job and did the Playboy shoot. Nice gal. But I digress...
Anyhoo, the only time I ever played with one of the spaceball units was when she let me try out her controller. My impression at the time was that there wasn't enough "snap" speed to them when I needed to do a 180. With a mouse, I can go from north to south in a single frame. I wasn't able to do that with the spaceball. So I elected not to pursue buying one.
Now, that was several years ago. It's possible that they've improved them now so that the feel is better. I haven't tried one in years. And I remember thinking at the time, "if I were a big-time Descent player, this controller would be indespensible." Alas, I was a Quake player and had no use for it.