My results were not so bad with them. I do prefer something more like LELO's Pleasure Beads and I know a lot of people have outstanding things to say about SmartBalls.
What material were the ones you tried? Were they glass or metal and therefore more slippery? There are other types made out of things like silicone which offer a bit more drag so they might not slide as easily. Also, the Pleasure Beads are quite a bit larger than the glass balls I have. (link