The listing you linked to says it is the lowest bouncing ball of the four. I would think that the softer ball would bounce less than the stiffer ones (maybe not!). I don't know if softer is better though for your purpose. Interesting idea.
It's kind of a crappy ad. I'd assume that the "intro" ball would be softer and slower/less bounce ball, while the "Pro" is the harder and faster one.