One of the best I have used is the one that is on the site I linked to earlier. It is made with plastic beads. I think it is the product that started that company. I have tried leather, but I don’t like them as much. I have seen them at sporting goods stores, but may even be in Walmart. When I was training in Martial arts I used to Jump Rope quite a bit. I just choped down the plastic bead rope I used to use for my daughter. The dogs had chewed a few of the beads, and it wasn’t working well at my length, but is like new again only shorter. Speed Rope
I’m sure an elite athlete like this found some improvement from doing heavy squats. There’s no doubt about this, doing this and many of the other exercises listed here will improve your jumping, but not anywhere to the extent that you would be lead to believe.
At the elite level, the contests are won by inches. There’s much less transfer from non-specific movements like this, but at this level the small improvements are what can bring them up to the top.
To get to your potential, you need to practice the movement to get the maximum amount of transfer. To jump higher, practice that type of jump! 
Avoid doing this at all costs!
Playing basketball with ankle weights is terribly destuctive to your joints. It also violates the specificity hypothesis.