My sweater shaver... worst $3.99 I ever spent at the grocery store.
I've not tried the sweater stone, but am curious now. I'd never heard of that before.
For my felting projects (which prompted me to purchase said sweater shaver), I've given up and gone for the more expedient and useful tool, the disposable double-blade ladies' razor. I can defuzz a handbag in under two minutes.