They sell a set with one 6x6x6 and one 3x3x3 neocube, so the 3x3x3 is for spares. Like the electronic bubble wrap toy I bought a few months back this will probable end up on the nightstand unused,
I don't know what the status of neocube.com is, but you can get industrial neodymium spheres on the internet pretty cheaply. I made a 4x4x4 cube with slightly larger spheres than these for about . It's a fun toy for the fidgety.